[CMake] Support for cross-compilation when build runtimes

When cross-compiling, we cannot use the just built toolchain, instead
we need to use the host toolchain which we assume has a support for
targeting the selected target platform. We also need to pass the path
to the native version of llvm-config to external projects.

Differential Revision: https://reviews.llvm.org/D41678

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322046 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/CrossCompile.cmake

@@ -50,6 +50,8 @@ function(llvm_create_cross_target_internal target_name toolchain buildtype)
         -DLLVM_TARGET_IS_CROSSCOMPILE_HOST=TRUE
         -DLLVM_TARGETS_TO_BUILD="${targets_to_build_arg}"
         -DLLVM_EXPERIMENTAL_TARGETS_TO_BUILD="${experimental_targets_to_build_arg}"
+        -DLLVM_DEFAULT_TARGET_TRIPLE="${TARGET_TRIPLE}"
+        -DLLVM_TARGET_ARCH="${LLVM_TARGET_ARCH}"
         ${build_type_flags} ${linker_flag} ${external_clang_dir}
     WORKING_DIRECTORY ${LLVM_${target_name}_BUILD}
     DEPENDS CREATE_LLVM_${target_name}

cmake/modules/LLVMExternalProjectUtils.cmake

@@ -102,7 +102,7 @@ function(llvm_ExternalProject_Add name source_dir)
     endforeach()
   endforeach()
 
-  if(ARG_USE_TOOLCHAIN)
+  if(ARG_USE_TOOLCHAIN AND NOT CMAKE_CROSSCOMPILING)
     if(CLANG_IN_TOOLCHAIN)
       set(compiler_args -DCMAKE_C_COMPILER=${LLVM_RUNTIME_OUTPUT_INTDIR}/clang
                         -DCMAKE_CXX_COMPILER=${LLVM_RUNTIME_OUTPUT_INTDIR}/clang++)
@@ -136,6 +136,16 @@ function(llvm_ExternalProject_Add name source_dir)
     set(sysroot_arg -DCMAKE_SYSROOT=${CMAKE_SYSROOT})
   endif()
 
+  if(CMAKE_CROSSCOMPILING)
+    set(compiler_args -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
+                      -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
+                      -DCMAKE_AR=${CMAKE_AR}
+                      -DCMAKE_RANLIB=${CMAKE_RANLIB})
+    set(llvm_config_path "${LLVM_NATIVE_BUILD}/bin/llvm-config")
+  else()
+    set(llvm_config_path "$<TARGET_FILE:llvm-config>")
+  endif()
+
   ExternalProject_Add(${name}
     DEPENDS ${ARG_DEPENDS} llvm-config
     ${name}-clobber
@@ -149,7 +159,7 @@ function(llvm_ExternalProject_Add name source_dir)
                -DCMAKE_INSTALL_PREFIX=${CMAKE_INSTALL_PREFIX}
                ${sysroot_arg}
                -DLLVM_BINARY_DIR=${PROJECT_BINARY_DIR}
-               -DLLVM_CONFIG_PATH=$<TARGET_FILE:llvm-config>
+               -DLLVM_CONFIG_PATH=${llvm_config_path}
                -DLLVM_ENABLE_WERROR=${LLVM_ENABLE_WERROR}
                -DLLVM_HOST_TRIPLE=${LLVM_HOST_TRIPLE}
                -DLLVM_HAVE_LINK_VERSION_SCRIPT=${LLVM_HAVE_LINK_VERSION_SCRIPT}

runtimes/CMakeLists.txt

@@ -354,6 +354,9 @@ else() # if this is included from LLVM's CMake
                              CMAKE_ARGS -DCOMPILER_RT_BUILD_BUILTINS=Off
                                         -DLLVM_INCLUDE_TESTS=${LLVM_INCLUDE_TESTS}
                                         -DLLVM_LIBRARY_DIR=${LLVM_LIBRARY_DIR}
+                                        -DCMAKE_C_COMPILER_TARGET=${TARGET_TRIPLE}
+                                        -DCMAKE_CXX_COMPILER_TARGET=${TARGET_TRIPLE}
+                                        -DCMAKE_ASM_COMPILER_TARGET=${TARGET_TRIPLE}
                                         -DCMAKE_C_COMPILER_WORKS=ON
                                         -DCMAKE_CXX_COMPILER_WORKS=ON
                                         -DCMAKE_ASM_COMPILER_WORKS=ON