[CMake][compiler-rt] Replace Windows backslashes with CMake ones

[phosek]

Summary

XRay builds uses llvm-config to obtain the ldflags and libs and then
passes those to CMake. Unfortunately, this breaks on Windows because
CMake tries to interpret backslashes followed by certain characters
as flags. We need to rewrite these into forward slashes that are used
by CMake (even on Windows).

[smeenai]

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

251–252

Does file(TO_CMAKE_PATH) work for this?

253

Why the addition of FORCE?

[phosek]

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

251–252

I tried it and it seems to work.

253

Leftover from debugging.

[phosek]

Ping?

[smeenai]

LGTM

At some point we should change this to use the LLVM CMake package instead of llvm-config, but that's way out of scope here, of course.

compiler-rt/cmake/Modules/CompilerRTUtils.cmake

execute_process(
       ERROR_QUIET)
     if (HAD_ERROR)
       message(WARNING "llvm-config finding xray failed with status ${HAD_ERROR}")
       set(COMPILER_RT_HAS_LLVMXRAY FALSE)
     else()
       string(REGEX REPLACE "[ \t]*[\r\n]+[ \t]*" ";" CONFIG_OUTPUT ${CONFIG_OUTPUT})
       list(GET CONFIG_OUTPUT 0 LDFLAGS)
       list(GET CONFIG_OUTPUT 1 LIBLIST)
-      set(LLVM_XRAY_LDFLAGS ${LDFLAGS} CACHE STRING "Linker flags for LLVMXRay library")
-      set(LLVM_XRAY_LIBLIST ${LIBLIST} CACHE STRING "Library list for LLVMXRay")
+      string(REPLACE "\\" "/" LDFLAGS ${LDFLAGS})
+      string(REPLACE "\\" "/" LIBLIST ${LIBLIST})
+      set(LLVM_XRAY_LDFLAGS ${LDFLAGS} CACHE STRING "Linker flags for LLVMXRay library" FORCE)
+      set(LLVM_XRAY_LIBLIST ${LIBLIST} CACHE STRING "Library list for LLVMXRay" FORCE)
       set(COMPILER_RT_HAS_LLVMXRAY TRUE)
     endif()
 
     set(COMPILER_RT_HAS_LLVMTESTINGSUPPORT FALSE)
     execute_process(
       COMMAND ${LLVM_CONFIG_PATH} "--ldflags" "--libs" "testingsupport"
       RESULT_VARIABLE HAD_ERROR
       OUTPUT_VARIABLE CONFIG_OUTPUT
       ERROR_QUIET)
     if (HAD_ERROR)
       message(WARNING "llvm-config finding testingsupport failed with status ${HAD_ERROR}")
     else()
       string(REGEX REPLACE "[ \t]*[\r\n]+[ \t]*" ";" CONFIG_OUTPUT ${CONFIG_OUTPUT})
       list(GET CONFIG_OUTPUT 0 LDFLAGS)
       list(GET CONFIG_OUTPUT 1 LIBLIST)
       if (LIBLIST STREQUAL "")
         message(WARNING "testingsupport library not installed, some tests will be skipped")
       else()
-        set(LLVM_TESTINGSUPPORT_LDFLAGS ${LDFLAGS} CACHE STRING "Linker flags for LLVMTestingSupport library")
-        set(LLVM_TESTINGSUPPORT_LIBLIST ${LIBLIST} CACHE STRING "Library list for LLVMTestingSupport")
+        string(REPLACE "\\" "/" LDFLAGS ${LDFLAGS})
+        string(REPLACE "\\" "/" LDFLAGS ${LIBLIST})
+        set(LLVM_TESTINGSUPPORT_LDFLAGS ${LDFLAGS} CACHE STRING "Linker flags for LLVMTestingSupport library" FORCE)
+        set(LLVM_TESTINGSUPPORT_LIBLIST ${LIBLIST} CACHE STRING "Library list for LLVMTestingSupport" FORCE)
         set(COMPILER_RT_HAS_LLVMTESTINGSUPPORT TRUE)
       endif()
     endif()
 
     # Make use of LLVM CMake modules.
     # --cmakedir is supported since llvm r291218 (4.0 release)
     execute_process(
       COMMAND ${LLVM_CONFIG_PATH} --cmakedir