Linking LLVM libraries on Windows with CMake and MinGW - c++

Question

I've been writing a compiler using LLVM as the backend. The CMake files I've written so far have worked on Linux, but I haven't had any luck on Windows. The project is split into a library and "driver" executable with their own CMakeLists.txt in separate subdirectories.
The top level CMakeLists.txt looks like this:
cmake_minimum_required (VERSION 3.7.0)
project (compiler)
set (CMAKE_CXX_STANDARD 14)
set (CMAKE_CXX_STANDARD_REQUIRED ON)
set (CMAKE_CXX_EXTENSIONS OFF)
find_package (LLVM REQUIRED CONFIG)
message (STATUS "Found LLVM ${LLVM_PACKAGE_VERSION}")
message (STATUS "Using LLVMConfig.cmake in: ${LLVM_DIR}")
include_directories (${LLVM_INCLUDE_DIRS})
add_definitions(${LLVM_DEFINITIONS})
add_subdirectory (Compiler_Lib)
add_subdirectory (Compiler_exe)
The CMakeLists.txt for the library:
cmake_minimum_required (VERSION 3.7.0)
add_library (compiler_lib
AST.cpp
AST.h
parser.cpp
parser.h
scanner.cpp
scanner.h
token.cpp
token.h
visualizer.cpp
visualizer.h
codegen.cpp
codegen.h)
target_include_directories (compiler_lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
target_link_libraries(compiler_lib LLVM)
And the CMakeLists.txt for the executable (which is where linking to the libraries fails):
cmake_minimum_required (VERSION 3.7.0)
project (compiler_exe)
add_executable (compiler_exe Compiler_exe.cpp getopt.h getopt.cpp)
target_link_libraries (compiler_exe LINK_PUBLIC LLVM compiler_lib)
I run the command "c:\Program Files\CMake\bin\cmake.exe" .. -G"MinGW Makefiles" -DCMAKE_PREFIX_PATH=C:\Users\James\llvm+clang-7.0.0-win64-msvc-release where C:\Users\James\llvm+clang-7.0.0-win64-msvc-release is the path to prebuilt LLVM libraries. However, running mingw32-make afterwards fails with the output
Scanning dependencies of target compiler_lib
[ 10%] Building CXX object Compiler_Lib/CMakeFiles/compiler_lib.dir/AST.cpp.obj
[ 20%] Building CXX object Compiler_Lib/CMakeFiles/compiler_lib.dir/parser.cpp.obj
[ 30%] Building CXX object Compiler_Lib/CMakeFiles/compiler_lib.dir/scanner.cpp.obj
[ 40%] Building CXX object Compiler_Lib/CMakeFiles/compiler_lib.dir/token.cpp.obj
[ 50%] Building CXX object Compiler_Lib/CMakeFiles/compiler_lib.dir/visualizer.cpp.obj
[ 60%] Building CXX object Compiler_Lib/CMakeFiles/compiler_lib.dir/codegen.cpp.obj
[ 70%] Linking CXX static library libcompiler_lib.a
[ 70%] Built target compiler_lib
Scanning dependencies of target compiler_exe
[ 80%] Building CXX object Compiler_exe/CMakeFiles/compiler_exe.dir/Compiler_exe.cpp.obj
[ 90%] Building CXX object Compiler_exe/CMakeFiles/compiler_exe.dir/getopt.cpp.obj
[100%] Linking CXX executable compiler_exe.exe
c:/mingw/bin/../lib/gcc/mingw32/8.2.0/../../../../mingw32/bin/ld.exe: cannot find -lLLVM
collect2.exe: error: ld returned 1 exit status
Compiler_exe\CMakeFiles\compiler_exe.dir\build.make:102: recipe for target 'Compiler_exe/compiler_exe.exe' failed
mingw32-make[2]: *** [Compiler_exe/compiler_exe.exe] Error 1
CMakeFiles\Makefile2:176: recipe for target 'Compiler_exe/CMakeFiles/compiler_exe.dir/all' failed
mingw32-make[1]: *** [Compiler_exe/CMakeFiles/compiler_exe.dir/all] Error 2
Makefile:82: recipe for target 'all' failed
mingw32-make: *** [all] Error 2
This is the first time I've used CMake so I could have missed something obvious, but as I say it seems to work on Linux.

Answer 1

For the linking to succeed two things need to be true:
1) the file libLLVM.a needs to exist
2) that file has to be in a directory in the library search path
There should be a way to get cmake to tell you the list of places it searches for libraries, and you need to find a way to get wherever libLLVM.a exists into that list of dirs.
Apologies for the partial answer, but that's the troubleshooting path...