[FMV][AArch64] Fix missing FMV defines for AArch64 in LNT Makefile

[IamYJLee]

Add conditional CFLAGS definitions for AArch64 targets to support FMV-related behavior on Darwin and Linux platforms.

• Adds -DHAS_DARWIN_FMV when ARCH=AArch64 and TARGET_OS=Darwin
• Adds -DHAS_LINUX_FMV when ARCH=AArch64 and TARGET_OS=Linux

This change fixes build errors when running LNT tests on AArch64 systems with platform-specific FMV handling.

This patch reflects the changes from llvm/llvm-test-suite@d24d5dcd.

ERROR CONTEXT

Before this patch, LNT test runs on AArch64 platforms (e.g., macOS arm64) could fail with missing symbol errors:

--- Tested: 140 tests --
FAIL: SingleSource/Benchmarks/Misc/aarch64-init-cpu-features.compile_time (1 of 140)
FAIL: SingleSource/Benchmarks/Misc/aarch64-init-cpu-features.execution_time (29 of 140)
Processing Times

Undefined symbols for architecture arm64:
  "_RUNTIME_INIT", referenced from:
      _main in aarch64-init-cpu-features.llvm.o
      _main in aarch64-init-cpu-features.llvm.o
      _main in aarch64-init-cpu-features.llvm.o
ld: symbol(s) not found for architecture arm64

[labrinea]

I am a bit puzzled with the equivalent cmake code

file(WRITE ${CMAKE_CURRENT_BINARY_DIR}/CheckHasAArch64FMV.h "void __init_cpu_features_resolver(void);")
check_symbol_exists(__init_cpu_features_resolver ${CMAKE_CURRENT_BINARY_DIR}/CheckHasAArch64FMV.h HAS_AARCH64_FMV)

The way I read it HAS_AARCH64_FMV is always true? Am I mistaken, do we need it here too perhaps? cc @jroelofs

[IamYJLee]

@labrinea Thank you for your comment.

I've confirmed how check_symbol_exists functions and understand that HAS_AARCH64_FMV is not always true. In my environment, when I configure the project using CMakeLists.txt, HAS_AARCH64_FMV is set to False.

However, when I run LNT with a Makefile that includes my modifications, the build and execution complete without any issues.

In other words, even though check_symbol_exists confirms that the __init_cpu_features_resolver symbol is missing, there are no problems compiling and running aarch64-init-cpu-features.c.