[libunwind] Add CMake support for building for MinGW

[mstorsjo]

Summary

This is the cmake specific parts of D33601 (by Martell Malone) split out into a separate patch, to ease getting this part reviewed indendent of the rest of that patch.

[compnerd]

With an explanation of the gcc_s vs gcc, I think this LG.

cmake/config-ix.cmake

38

This seems really weird. gcc_s and gcc are the same library, the former is the shared version of the latter. Is this really correct?

[mstorsjo]

cmake/config-ix.cmake

38

I think so; my impression is that libgcc.a contains some object files that end up linked into every module, even if you're otherwise using a shared libgcc_s_<ehmode>.dll.

In any case, this is identical to the same lines in libcxxabi and libcxx as well; the only difference is in the library name above in if (<libname>_USE_COMPILER_RT), so if there needs to be a change, it should be changed there as well.

cmake/config-ix.cmake

if (LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
   endif ()
   if (LIBUNWIND_USE_COMPILER_RT)
     list(APPEND CMAKE_REQUIRED_FLAGS -rtlib=compiler-rt)
     find_compiler_rt_library(builtins LIBUNWIND_BUILTINS_LIBRARY)
     list(APPEND CMAKE_REQUIRED_LIBRARIES "${LIBUNWIND_BUILTINS_LIBRARY}")
   elseif (LIBUNWIND_HAS_GCC_S_LIB)
     list(APPEND CMAKE_REQUIRED_LIBRARIES gcc_s)
   endif ()
+  if (MINGW)
+    # Mingw64 requires quite a few "C" runtime libraries in order for basic
+    # programs to link successfully with -nodefaultlibs.
+    if (LIBUNWIND_USE_COMPILER_RT)
+      set(MINGW_RUNTIME ${LIBUNWIND_BUILTINS_LIBRARY})
+    else ()
+      set(MINGW_RUNTIME gcc_s gcc)
+    endif()
+    set(MINGW_LIBRARIES mingw32 ${MINGW_RUNTIME} moldname mingwex msvcrt advapi32
+                        shell32 user32 kernel32 mingw32 ${MINGW_RUNTIME}
+                        moldname mingwex msvcrt)
+    list(APPEND CMAKE_REQUIRED_LIBRARIES ${MINGW_LIBRARIES})
+  endif()
   if (CMAKE_C_FLAGS MATCHES -fsanitize OR CMAKE_CXX_FLAGS MATCHES -fsanitize)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize=all")
   endif ()
   if (CMAKE_C_FLAGS MATCHES -fsanitize-coverage OR CMAKE_CXX_FLAGS MATCHES -fsanitize-coverage)
     set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -fno-sanitize-coverage=edge,trace-cmp,indirect-calls,8bit-counters")
   endif ()
 endif ()