How to cross-compile Clang on Ubuntu for Win32? - cmake

Question

I downloaded & extracted:
http://releases.llvm.org/5.0.1/llvm-5.0.1.src.tar.xz
http://releases.llvm.org/5.0.1/cfe-5.0.1.src.tar.xz
Then:
$ mv cfe-5.0.1.src llvm-5.0.1.src/tool/clang
Created the following llvm-5.0.1.src/mingw_cross_toolchain.cmake file:
set(CMAKE_SYSTEM_NAME Windows)
set(TOOLCHAIN_PREFIX x86_64-w64-mingw32)
# cross compilers to use for C and C++
set(CMAKE_C_COMPILER ${TOOLCHAIN_PREFIX}-gcc-posix)
set(CMAKE_CXX_COMPILER ${TOOLCHAIN_PREFIX}-g++-posix)
set(CMAKE_Fortran_COMPILER ${TOOLCHAIN_PREFIX}-gfortran)
set(CMAKE_RC_COMPILER ${TOOLCHAIN_PREFIX}-windres)
# target environment on the build host system
# set 1st to dir with the cross compiler's C/C++ headers/libs
set(CMAKE_FIND_ROOT_PATH /usr/lib/gcc/${TOOLCHAIN_PREFIX}/7.3-posix)
# modify default behavior of FIND_XXX() commands to
# search for headers/libs in the target environment and
# search for programs in the build host environment
set(CMAKE_FIND_ROOT_PATH_MODE_PROGRAM NEVER)
set(CMAKE_FIND_ROOT_PATH_MODE_LIBRARY ONLY)
set(CMAKE_FIND_ROOT_PATH_MODE_INCLUDE ONLY)
Then:
$ cd llvm-5.0.1.src
$ mkdir build
# cd build
$ cmake -D CMAKE_TOOLCHAIN_FILE=../mingw_cross_toolchain.cmake
Then in the following build/NATIVE/include/llvm/Config/llvm-config.h I have:
/* Define if this is Unixish platform */
#define LLVM_ON_UNIX 1
/* Define if this is Win32ish platform */
/* #undef LLVM_ON_WIN32 */
Which will make the build fail. Since LLVM_ON_WIN32 depends on the WIN32 flag, I tried to define that flag on the command line and in the mingw_cross_toolchain.cmake but alas with no effect on the generated build/NATIVE/include/llvm/Config/llvm-config.h.
How can we define that WIN32 flag properly?

Answer 1

Ok so I need to force by setting the flags in cmake/modules/HandleLLVMOptions.cmake to:
set(WIN32 1)
set(UNIX 0)
Then I need to be able to execute the future intermediate Win32 executables:
$ sudo apt-get install wine-binfmt
$ sudo update-binfmts --import /usr/share/binfmts/wine
After that I need to set the WINEPATH to find the DLLs:
$ export WINEPATH="/usr/x86_64-w64-mingw32/lib/;/usr/lib/gcc/x86_64-w64-mingw32/7.3-posix"
Now I'll be able to cross-compile everything properly!