Add CMake support for building for MinGW

This section is similar to what already exists in libcxx and libcxxabi.

Differential Revision: https://reviews.llvm.org/D38380

llvm-svn: 314716

libunwind/cmake/config-ix.cmake

@@ -29,6 +29,19 @@ if (LIBUNWIND_HAS_NODEFAULTLIBS_FLAG)
   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 ()