Update CMake toolchain file for Windows and CMAKE_AR (#297)

1. Use exe suffix to find clang on Windows
2. Only set the tools if they are not already overridden (for some reason this is required for CMAKE_AR and CMAKE_RANLIB to work).
3. Pass --target by default for proper auto-detection of the target platform.

Author: dschuff

src/build.py

@@ -1168,9 +1168,6 @@ def CompilerRT():
              '-DCMAKE_TOOLCHAIN_FILE=' +
              os.path.join(INSTALL_DIR, 'wasm_standalone.cmake'),
              '-DCMAKE_C_COMPILER_WORKS=ON',
-             # TODO: why doesn't setting CMAKE_AR in the toolchain file work?
-             '-DCMAKE_AR=' + os.path.join(INSTALL_BIN, 'llvm-ar'),
-             '-DCMAKE_RANLIB=' + os.path.join(INSTALL_BIN, 'llvm-ranlib'),
              '-DCOMPILER_RT_BAREMETAL_BUILD=On',
              '-DCOMPILER_RT_BUILD_XRAY=OFF',
              '-DCOMPILER_RT_INCLUDE_TESTS=OFF',

src/wasm_standalone.cmake

@@ -9,12 +9,28 @@ set(CMAKE_SYSTEM_PROCESSOR wasm32)
 set(triple wasm32-unknown-unknown-wasm)
 
 set(WASM_SDKROOT ${CMAKE_CURRENT_LIST_DIR})
-set(CMAKE_C_COMPILER ${WASM_SDKROOT}/bin/clang)
-set(CMAKE_CXX_COMPILER ${WASM_SDKROOT}/bin/clang++)
-set(CMAKE_AR ${WASM_SDKROOT}/bin/llvm-ar)
-set(CMAKE_RANLIB ${WASM_SDKROOT}/bin/llvm-ranlib)
+
+if (CMAKE_HOST_WIN32)
+        set(EXE_SUFFIX ".exe")
+else()
+        set(EXE_SUFFIX "")
+endif()
+if ("${CMAKE_C_COMPILER}" STREQUAL "")
+  set(CMAKE_C_COMPILER ${WASM_SDKROOT}/bin/clang${EXE_SUFFIX})
+endif()
+if ("${CMAKE_CXX_COMPILER}" STREQUAL "")
+  set(CMAKE_CXX_COMPILER ${WASM_SDKROOT}/bin/clang++${EXE_SUFFIX})
+endif()
+if ("${CMAKE_AR}" STREQUAL "")
+  set(CMAKE_AR ${WASM_SDKROOT}/bin/llvm-ar${EXE_SUFFIX} CACHE FILEPATH "llvm ar")
+endif()
+if ("${CMAKE_RANLIB}" STREQUAL "")
+ set(CMAKE_RANLIB ${WASM_SDKROOT}/bin/llvm-ranlib${EXE_SUFFIX} CACHE FILEPATH "llvm ranlib")
+endif()
 set(CMAKE_C_COMPILER_TARGET ${triple})
 set(CMAKE_CXX_COMPILER_TARGET ${triple})
+set(CMAKE_C_FLAGS --target=${triple})
+set(CMAKE_CXX_FLAGS --target=${triple})
 
 set(CMAKE_SYSROOT ${WASM_SDKROOT}/sysroot)
 set(CMAKE_STAGING_PREFIX ${WASM_SDKROOT}/sysroot)