[CMake] Rudimentary support for standalone CompilerRT build system.

This change allows to build compiler-rt libraries separately from
LLVM/Clang (path to LLVM build directory should be specified at
configure time). Running tests is not yet supported.

llvm-svn: 201647
diff --git a/compiler-rt/cmake/Modules/CompilerRTUtils.cmake b/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
index fc1da85..ae2d608 100644
--- a/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
+++ b/compiler-rt/cmake/Modules/CompilerRTUtils.cmake
@@ -18,7 +18,7 @@
 # Check if a given flag is present in a space-separated flag_string.
 # Store the result in out_var.
 function(find_flag_in_string flag_string flag out_var)
-  string(REPLACE " " ";" flag_list ${flag_string})
+  string(REPLACE " " ";" flag_list "${flag_string}")
   list(FIND flag_list ${flag} flag_pos)
   if(NOT flag_pos EQUAL -1)
     set(${out_var} TRUE PARENT_SCOPE)