Fix build issues when compiling WAMRC as a cross-compiler

[peter-tatrai]

Description

This pull request addresses issues encountered when compiling WAMRC to be a cross-compiler—running on a PC while targeting an embedded ARM platform. The key fixes include:

Fixes in This PR

• -m32 compiler flag

  • The -m32 flag was previously added unconditionally for 32-bit targets, causing issues for non-x86 platforms.
  • Now, -m32 is only added when targeting a 32-bit x86 platform (X86_32), ensuring it is only applied where supported.

• Improved PIC Flag Handling:

  • The logic for setting PIC (-fPIC) based on WAMR_BUILD_PLATFORM was overly complex.
  • This is now handled in CMake instead of using platform-specific conditions.

• AOT Relocation Functions:

  • WAMRC previously included platform-specific headers (e.g., <arm_neon.h>) that are not available on a PC.
  • Since these AOT relocation functions are only used when executing AOT-compiled code (not by WAMRC itself), dummy versions have been introduced.
  • A more complete solution would be to split the code to avoid linking these functions altogether, but that would require more extensive changes.

• SIMD Compilation Issues:

  • WAMRC attempted to include target platform-specific SIMD headers (e.g., ARM headers) when compiling on a different host platform (e.g., x86).
  • To address this, an option has been added to disable SIMD in WAMRC when cross-compiling.

[calvin2021y]

hi @peter-tatrai

<arm_neon.h> is required at runtime ? if so maybe allow user set sysroot and triple by args will fix the problem.

[peter-tatrai]

The header file is required at compile-time, but this is not about cross-compiling wamrc—rather, it's about building a cross-compiler. In this scenario, we have both a host and a target architecture (e.g., host: x86_64, target: armv7). However, the CMake files currently use a single variable, WAMR_BUILD_PLATFORM, for both, even though it should only define the target platform. This causes issues, such as the one mentioned above.

With these commits and -DWAMR_BUILD_INVOKE_NATIVE_GENERAL=1 -DWAMR_BUILD_SIMD=0 -DWAMR_BUILD_TARGET=ARMv7, it is possible to build wamrc as a runnable binary on a PC while cross-compiling AOT modules for armv7.