When compiling without a specified --edition, emit a note

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[estebank]

I'll try to write an MCP later (unless someone does it for me). This change was motivated after seeing https://internals.rust-lang.org/t/code-compiles-on-playground-but-fails-when-passed-via-stdin-to-rustc/24393 where the different defaults between cargo, playground and rustc caused people to get confused.

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Some changes occurred in src/tools/compiletest

cc @jieyouxu

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[rust-log-analyzer]

The job aarch64-gnu-llvm-21-1 failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[TIMING:end] tool::ToolBuild { build_compiler: Compiler { stage: 1, host: aarch64-unknown-linux-gnu, forced_compiler: false }, target: aarch64-unknown-linux-gnu, tool: "error_index_generator", path: "src/tools/error_index_generator", mode: ToolRustcPrivate, source_type: InTree, extra_features: [], allow_features: "", cargo_args: [], artifact_kind: Binary } -- 60.442
[TIMING:end] tool::ErrorIndex { compilers: RustcPrivateCompilers { build_compiler: Compiler { stage: 1, host: aarch64-unknown-linux-gnu, forced_compiler: false }, target_compiler: Compiler { stage: 2, host: aarch64-unknown-linux-gnu, forced_compiler: false } } } -- 0.000
##[group]Testing stage2 error-index (aarch64-unknown-linux-gnu)
##[endgroup]
note: `--edition` is unspecified, defaulting to `2015` while the latest is `2024`; it must be one of: <2015|2018|2021|2024|future>


running 1117 tests
test /checkout/obj/build/aarch64-unknown-linux-gnu/test/error-index.md - Rust_Compiler_Error_Index::E0004 (line 67) - compile fail ... ok
test /checkout/obj/build/aarch64-unknown-linux-gnu/test/error-index.md - Rust_Compiler_Error_Index::E0002::_::Note__this_error_code_is_no_longer_emitted_by_the_compiler_ (line 51) - compile fail ... ok
---
---- [run-make] tests/run-make/const-destruct-stable-toolchain stdout ----

error: rmake recipe failed to complete
status: exit status: 101
command: cd "/checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make/const-destruct-stable-toolchain/rmake_out" && env -u RUSTFLAGS -u __STD_REMAP_DEBUGINFO_ENABLED AR="ar" BUILD_ROOT="/checkout/obj/build/aarch64-unknown-linux-gnu" CC="cc" CC_DEFAULT_FLAGS="-ffunction-sections -fdata-sections -fPIC" CXX="c++" CXX_DEFAULT_FLAGS="-ffunction-sections -fdata-sections -fPIC" HOST_RUSTC_DYLIB_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/lib" LD_LIBRARY_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/bootstrap-tools/aarch64-unknown-linux-gnu/release/build/run_make_support/81c3418404f46bf6/out:/checkout/obj/build/aarch64-unknown-linux-gnu/stage0/lib/rustlib/aarch64-unknown-linux-gnu/lib" LD_LIB_PATH_ENVVAR="LD_LIBRARY_PATH" LLVM_BIN_DIR="/usr/lib/llvm-21/bin" LLVM_COMPONENTS="aarch64 aarch64asmparser aarch64codegen aarch64desc aarch64disassembler aarch64info aarch64utils aggressiveinstcombine all all-targets amdgpu amdgpuasmparser amdgpucodegen amdgpudesc amdgpudisassembler amdgpuinfo amdgputargetmca amdgpuutils analysis arm armasmparser armcodegen armdesc armdisassembler arminfo armutils asmparser asmprinter avr avrasmparser avrcodegen avrdesc avrdisassembler avrinfo binaryformat bitreader bitstreamreader bitwriter bpf bpfasmparser bpfcodegen bpfdesc bpfdisassembler bpfinfo cfguard cgdata codegen codegentypes core coroutines coverage debuginfobtf debuginfocodeview debuginfodwarf debuginfodwarflowlevel debuginfogsym debuginfologicalview debuginfomsf debuginfopdb demangle dlltooldriver dwarfcfichecker dwarflinker dwarflinkerclassic dwarflinkerparallel dwp engine executionengine extensions filecheck frontendatomic frontenddirective frontenddriver frontendhlsl frontendoffloading frontendopenacc frontendopenmp fuzzercli fuzzmutate globalisel hexagon hexagonasmparser hexagoncodegen hexagondesc hexagondisassembler hexagoninfo hipstdpar instcombine instrumentation interfacestub interpreter ipo irprinter irreader jitlink lanai lanaiasmparser lanaicodegen lanaidesc lanaidisassembler lanaiinfo libdriver lineeditor linker loongarch loongarchasmparser loongarchcodegen loongarchdesc loongarchdisassembler loongarchinfo lto m68k m68kasmparser m68kcodegen m68kdesc m68kdisassembler m68kinfo mc mca mcdisassembler mcjit mcparser mips mipsasmparser mipscodegen mipsdesc mipsdisassembler mipsinfo mirparser msp430 msp430asmparser msp430codegen msp430desc msp430disassembler msp430info native nativecodegen nvptx nvptxcodegen nvptxdesc nvptxinfo objcarcopts objcopy object objectyaml option orcdebugging orcjit orcshared orctargetprocess passes perfjitevents powerpc powerpcasmparser powerpccodegen powerpcdesc powerpcdisassembler powerpcinfo profiledata remarks riscv riscvasmparser riscvcodegen riscvdesc riscvdisassembler riscvinfo riscvtargetmca runtimedyld sandboxir scalaropts selectiondag sparc sparcasmparser sparccodegen sparcdesc sparcdisassembler sparcinfo spirv spirvanalysis spirvcodegen spirvdesc spirvinfo support symbolize systemz systemzasmparser systemzcodegen systemzdesc systemzdisassembler systemzinfo tablegen target targetparser telemetry textapi textapibinaryreader transformutils ve veasmparser vecodegen vectorize vedesc vedisassembler veinfo webassembly webassemblyasmparser webassemblycodegen webassemblydesc webassemblydisassembler webassemblyinfo webassemblyutils windowsdriver windowsmanifest x86 x86asmparser x86codegen x86desc x86disassembler x86info x86targetmca xcore xcorecodegen xcoredesc xcoredisassembler xcoreinfo xray xtensa xtensaasmparser xtensacodegen xtensadesc xtensadisassembler xtensainfo" LLVM_FILECHECK="/usr/lib/llvm-21/bin/FileCheck" NODE="/usr/bin/node" PYTHON="/usr/bin/python3" RUSTC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" RUSTDOC="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustdoc" SOURCE_ROOT="/checkout" TARGET="aarch64-unknown-linux-gnu" TARGET_EXE_DYLIB_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/lib/rustlib/aarch64-unknown-linux-gnu/lib" __BOOTSTRAP_JOBS="4" __RMAKE_VERBOSE_SUBPROCESS_OUTPUT="1" __RUSTC_DEBUG_ASSERTIONS_ENABLED="1" __STD_DEBUG_ASSERTIONS_ENABLED="1" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make/const-destruct-stable-toolchain/rmake"
stdout: none
--- stderr -------------------------------
LD_LIBRARY_PATH="/checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make/const-destruct-stable-toolchain/rmake_out:/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/lib:/checkout/obj/build/aarch64-unknown-linux-gnu/bootstrap-tools/aarch64-unknown-linux-gnu/release/build/run_make_support/81c3418404f46bf6/out:/checkout/obj/build/aarch64-unknown-linux-gnu/stage0/lib/rustlib/aarch64-unknown-linux-gnu/lib" RUSTC_BOOTSTRAP="-1" "/checkout/obj/build/aarch64-unknown-linux-gnu/stage2/bin/rustc" "-L" "/checkout/obj/build/aarch64-unknown-linux-gnu/test/run-make/const-destruct-stable-toolchain/rmake_out" "const-drop.rs" "--target=aarch64-unknown-linux-gnu"
output status: `exit status: 1`
=== STDOUT ===



=== STDERR ===
note: `--edition` is unspecified, defaulting to `2015` while the latest is `2024`; it must be one of: <2015|2018|2021|2024|future>

error[E0493]: destructor of `T` cannot be evaluated at compile-time
##[error] --> const-drop.rs:1:24
  |
1 | const fn const_drop<T>(_: T) {}
---

--- const-drop-stable.stderr
+++ (rustc)
@@ -1,3 +1,5 @@
+note: `--edition` is unspecified, defaulting to `2015` while the latest is `2024`; it must be one of: <2015|2018|2021|2024|future>
+
 error[E0493]: destructor of `T` cannot be evaluated at compile-time
  --> const-drop.rs:1:24
   |