[cmake] Install 'clang-cpp' symlink

Install the 'clang-cpp' symlink used to spawn the preprocessor. The code
handling this suffix is already included in Driver. FreeBSD is already
creating such a symlink in ports, and a similar one was requested
by Gentoo/FreeBSD team. The goal is to handle software that takes a C
preprocessor via a variable but does not handle passing options
correctly (i.e. 'clang -E' does not work).

Bug: https://bugs.gentoo.org/478810

Differential Revision: https://reviews.llvm.org/D25161

llvm-svn: 283075

clang/tools/driver/CMakeLists.txt

@@ -52,7 +52,7 @@ endif()
 add_dependencies(clang clang-headers)
 
 if(NOT CLANG_LINKS_TO_CREATE)
-  set(CLANG_LINKS_TO_CREATE clang++ clang-cl)
+  set(CLANG_LINKS_TO_CREATE clang++ clang-cl clang-cpp)
 
   if (WIN32)
     list(APPEND CLANG_LINKS_TO_CREATE ../msbuild-bin/cl)