Fix detection of whether long double is the same as double

One change in PR 305 was not quite right: it changed a check for whether
`$(ARCH)` is `aarch64` to a check for whether it's `aarch64 riscv64`,
which can never be true. It was a non-functional change on RISC-V (since
it can't be true) but broke AArch64, at least for FreeBSD. Notably,
changing the check to what I assume was intended, i.e. `aarch64` or
`riscv64`, breaks RISC-V. So this commit instead reverts this one change
in 305.

Author: ararslan

Make.inc

@@ -171,7 +171,7 @@ ifneq ($(filter $(ARCH),i387 amd64),)
 # linux x86_64, for instance, `long double` is 80 bits wide, whereas on macOS aarch64,
 # `long double` is the same as `double`. 
 LONG_DOUBLE_NOT_DOUBLE := 1
-else ifeq ($(ARCH), aarch64 riscv64)
+else ifeq ($(ARCH), aarch64)
 ifeq ($(filter $(OS),Darwin WINNT),)
 LONG_DOUBLE_NOT_DOUBLE := 1
 endif