test: introduce new target-swiftxx-frontend for C++ interop

Add an convert to the new `target-swiftxx-frontend` substitution in lit
to control the C++ interop enabling in Swift.  This allows for a single
site which will enable control of both an overridden standard (for
testing multiple C++ standards) and simplify writing tests.

Author: compnerd

test/ClangImporter/cxx_interop.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -typecheck %s -I %S/Inputs/custom-modules -module-cache-path %t -enable-cxx-interop
+// RUN: %target-swiftxx-frontend -typecheck %s -I %S/Inputs/custom-modules
 
 import CXXInterop
 

test/ClangImporter/cxx_interop_ir.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -module-name cxx_ir -I %S/Inputs/custom-modules -module-cache-path %t -enable-cxx-interop -emit-ir -o - -primary-file %s | %FileCheck %s
+// RUN: %target-swiftxx-frontend -module-name cxx_ir -I %S/Inputs/custom-modules -emit-ir -o - -primary-file %s | %FileCheck %s
 
 import CXXInterop
 

test/ClangImporter/enum-cxx.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -emit-ir -primary-file %s -I %S/Inputs/custom-modules -module-cache-path %t -enable-cxx-interop -o - | %FileCheck %s
+// RUN: %target-swiftxx-frontend -emit-ir -primary-file %s -I %S/Inputs/custom-modules -o - | %FileCheck %s
 
 import CXXInterop
 

test/Interop/C/function/emit-called-inline-function-irgen.swift

@@ -6,7 +6,7 @@
 
 // RUN: %empty-directory(%t)
 // RUN: %target-swift-frontend %s -I %S/Inputs -Xcc -std=c99 -emit-ir -o - | %FileCheck %s -check-prefix C99 --implicit-check-not notCalled
-// RUN: %target-swift-frontend %s -I %S/Inputs -enable-cxx-interop -emit-ir -o - | %FileCheck %s -check-prefix CXX --implicit-check-not notCalled
+// RUN: %target-swiftxx-frontend %s -I %S/Inputs -emit-ir -o - | %FileCheck %s -check-prefix CXX --implicit-check-not notCalled
 
 import EmitCalledInlineFunction
 

test/Interop/Cxx/class/constructors-silgen.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -I %S/Inputs -enable-cxx-interop -emit-silgen %s | %FileCheck %s
+// RUN: %target-swiftxx-frontend -I %S/Inputs -emit-silgen %s | %FileCheck %s
 
 import Constructors
 

test/Interop/Cxx/class/debug-info-irgen.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -enable-cxx-interop -I %S/Inputs %s -emit-ir -g | %FileCheck %s
+// RUN: %target-swiftxx-frontend -I %S/Inputs %s -emit-ir -g | %FileCheck %s
 
 // Validate that we don't crash when trying to deserialize C++ type debug info.
 // Note, however, that the actual debug info is not generated, see SR-13223.

test/Interop/Cxx/class/memory-layout-silgen.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -I %S/Inputs -enable-cxx-interop -emit-ir -o - %s | %FileCheck %s
+// RUN: %target-swiftxx-frontend -I %S/Inputs -emit-ir -o - %s | %FileCheck %s
 
 import MemoryLayout
 

test/Interop/Cxx/class/type-classification-non-trivial-irgen.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -enable-cxx-interop -I %S/Inputs %s -emit-ir | %FileCheck %s
+// RUN: %target-swiftxx-frontend -I %S/Inputs %s -emit-ir | %FileCheck %s
 
 // Verify that non-trival/address-only C++ classes are constructed and accessed
 // correctly. Make sure that we correctly IRGen functions that construct

test/Interop/Cxx/class/type-classification-non-trivial-silgen.swift

@@ -1,4 +1,4 @@
-// RUN: %target-swift-frontend -I %S/Inputs -enable-cxx-interop -emit-silgen %s | %FileCheck %s
+// RUN: %target-swiftxx-frontend -I %S/Inputs -emit-silgen %s | %FileCheck %s
 
 import TypeClassification
 

test/Interop/Cxx/implementation-only-imports/check-constructor-visibility-inversed.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-swift-frontend -emit-module -o %t/FortyTwo.swiftmodule -I %S/Inputs %s -enable-cxx-interop
+// RUN: %target-swiftxx-frontend -emit-module -o %t/FortyTwo.swiftmodule -I %S/Inputs %s
 
 // Swift should consider all sources for a decl and recognize that the
 // decl is not hidden behind @_implementationOnly in all modules.