[cmake] Turns out ClangTargets.cmake can also be in $CLANG_BUILD/lib/cmake/clang.

LLVM's cmake path has this extra path (for LLVM) as well. I should have followed
its example. = /.

rdar://26154980

Author: gottesmm

cmake/modules/SwiftSharedCMakeConfig.cmake

@@ -122,7 +122,8 @@ macro(swift_common_standalone_build_config_clang product is_cross_compiling)
 
   # Add all Clang CMake paths to our cmake module path.
   set(SWIFT_CLANG_CMAKE_PATHS
-    "${PATH_TO_CLANG_BUILD}/share/clang/cmake")
+    "${PATH_TO_CLANG_BUILD}/share/clang/cmake"
+    "${PATH_TO_CLANG_BUILD}/lib/cmake/clang")
   foreach(path ${SWIFT_CLANG_CMAKE_PATHS})
     list(APPEND CMAKE_MODULE_PATH ${path})
   endforeach()