[CMake] fix CLANG_INCLUDE_DIRS CMake export

Summary:
This change should fixes the export of CLANG_INCLUDE_DIRS variable in ClangConfig.cmake.

Unlike for the other variables, CLANG_INSTALL_PREFIX wasn't escaped meaning CLANG_INCLUDE_DIRS
resulting in the path "/include" instead of "${CLANG_INSTALL_PREFIX}/include".

Reviewers: beanz

Subscribers: mgorny

Differential Revision: https://reviews.llvm.org/D30911

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@298424 91177308-0d34-0410-b5e6-96231b3b80d8

cmake/modules/CMakeLists.txt

@@ -42,7 +42,7 @@ set(CLANG_CONFIG_CMAKE_DIR "\${CLANG_INSTALL_PREFIX}/${CLANG_INSTALL_PACKAGE_DIR
 set(CLANG_CONFIG_LLVM_CMAKE_DIR "\${CLANG_INSTALL_PREFIX}/${LLVM_INSTALL_PACKAGE_DIR}")
 set(CLANG_CONFIG_EXPORTS_FILE "\${CLANG_CMAKE_DIR}/ClangTargets.cmake")
 set(CLANG_CONFIG_INCLUDE_DIRS
-  "${CLANG_INSTALL_PREFIX}/include"
+  "\${CLANG_INSTALL_PREFIX}/include"
   )
 configure_file(
   ${CMAKE_CURRENT_SOURCE_DIR}/ClangConfig.cmake.in