Reland "[CMake][compiler-rt] Mark libcxx build  for tsan as standalone"

This relands commit r291722.

llvm-svn: 292083
diff --git a/compiler-rt/cmake/Modules/AddCompilerRT.cmake b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
index 3c1e1c1..d4533e6 100644
--- a/compiler-rt/cmake/Modules/AddCompilerRT.cmake
+++ b/compiler-rt/cmake/Modules/AddCompilerRT.cmake
@@ -380,6 +380,7 @@
                -DCMAKE_BUILD_TYPE=Release
                -DCMAKE_INSTALL_PREFIX:PATH=<INSTALL_DIR>
                -DLLVM_PATH=${LLVM_MAIN_SRC_DIR}
+               -DLIBCXX_STANDALONE_BUILD=On
     LOG_BUILD 1
     LOG_CONFIGURE 1
     LOG_INSTALL 1