feat: make enable_cross_compiler more open-closed

[abeimler]

Another remaining issue for Cross-compiling is that its options are using global CMake options instead of the function arguments. We should be using function arguments

#180 (comment)

# my custom arm settings
  enable_cross_compiler(
    CC "arm-none-eabi-gcc"
    CXX "arm-none-eabi-g++"
    TARGET_ARCHITECTURE "arm"
    CROSS_ROOT "/usr/arm-none-eabi-gcc"
    CROSS_TRIPLET "arm-none-eabi-gcc"
  )  

# opt-in cross-compiling
if(ENABLE_AARCH64_CROSS_COMPILING)
  # my custom aarch64 settings
  enable_cross_compiler(
    DEFAULT_TRIPLET "arm64-linux"
    CC "aarch64-linux-gnu-gcc"
    CXX "aarch64-linux-gnu-g++"
    TARGET_ARCHITECTURE "arm64-linux"
    CROSS_ROOT "/usr/gcc-aarch64-linux-gnu"
    CROSS_TRIPLET "aarch64-linux-gnu"
    #TOOLCHAIN_FILE "${CMAKE_CURRENT_SOURCE_DIR}/cmake/my-toolchain.cmake"
  )
else()
  option(ENABLE_CROSS_COMPILING "Detect cross compiler and setup toolchain" OFF)
  if(ENABLE_CROSS_COMPILING)
    enable_cross_compiler()
  endif()
endif()

[abeimler]

fatal error: stdio.h: No such file or directory

idk why the CI failed last time Q-Q ... it worked in docker and in the last CI-PR-Check (maybe some caching problem...)

Anyway, I rewrite the example(s) and make it more "bare metal".

[abeimler]

#180 (comment)

I try to auto-detect the following cross-compilers, when setting DEFAULT_TRIPLET:

• mingw-w64 x86_64-w64-mingw32.toolchain.cmake
• emscripten

Example:

• -DENABLE_CROSS_COMPILING:BOOL=ON -DDEFAULT_TRIPLET=x64-mingw-dynamic
• -DENABLE_CROSS_COMPILING:BOOL=ON -DDEFAULT_TRIPLET=wasm32-emscripten

For arm-linux or arm64-linux, you must set the compiler:

• aarch64-linux-gnu aarch64-linux.toolchain.cmake
• arm-linux-gnueabi, arm-linux-gnueabihf arm-linux.toolchain.cmake

Example:

• -DENABLE_CROSS_COMPILING:BOOL=ON -DCMAKE_C_COMPILER=gcc-aarch64-linux-gnu-gcc -DCMAKE_CXX_COMPILER=gcc-aarch64-linux-gnu-g++ -DDEFAULT_TRIPLET=arm64-linux
• -DENABLE_CROSS_COMPILING:BOOL=ON -DCMAKE_C_COMPILER=arm-linux-gnueabihf-gcc -DCMAKE_CXX_COMPILER=arm-linux-gnueabi-g++ -DDEFAULT_TRIPLET=arm-linux -DCROSS_ROOT=/usr/gcc-arm-linux-gnueabihf

For (bare-metal) you don't need/can't(?) set arm-linux/arm64-linux (for vcpkg):

• arm-none-eabi arm.toolchain.cmake

Example:

• -DENABLE_CROSS_COMPILING:BOOL=ON -DCMAKE_C_COMPILER=arm-none-eabi-gcc -DCMAKE_CXX_COMPILER=arm-none-eabi-g++
• -DENABLE_CROSS_COMPILING:BOOL=ON -DCMAKE_C_COMPILER=arm-none-eabi-gcc -DCMAKE_CXX_COMPILER=arm-none-eabi-g++ -DTARGET_ARCHITECTURE:STRING=arm -DCROSS_ROOT:STRING="/usr/arm-none-eabi-gcc" -DCROSS_TRIPLET:STRING=arm-none-eabi-gcc

The option for DEFAULT_TRIPLET are the simlary to vcpkg triplets

• x64-mingw-dynamic
• x64-mingw-static
• x86-mingw-dynamic
• x86-mingw-static
• wasm32-emscripten
• arm-linux
• arm64-linux

[aminya]

Thanks for the changes!