build: include more directories

llvm/Support/Compiler.h recently grew a dependency on llvm-config.h.  This
pointed out that we were not including the path to the generated header
directory in the build output.  Ensure that we have the corresponding -I.

Author: compnerd

cmake/modules/SwiftSharedCMakeConfig.cmake

@@ -252,6 +252,9 @@ macro(swift_common_standalone_build_config product is_cross_compiling)
                       "${CLANG_MAIN_INCLUDE_DIR}"
                       "${CMARK_MAIN_INCLUDE_DIR}"
                       "${CMARK_BUILD_INCLUDE_DIR}")
+  foreach (INCLUDE_DIR ${LLVM_INCLUDE_DIRS})
+    include_directories(${INCLUDE_DIR})
+  endforeach ()
 
   link_directories(
       "${LLVM_LIBRARY_DIR}"