build: don't always load clang/cmark

clang/cmark are only needed for the tools, not for the runtime/SDK
overlay.  Do not attempt to configure clang and CMark in the case we do
not build the tools.  This is needed to enable the standalone standard
library only builds.

Author: compnerd

cmake/modules/SwiftSharedCMakeConfig.cmake

@@ -196,13 +196,12 @@ endmacro()
 #   product
 #     The product name, e.g. Swift or SourceKit. Used as prefix for some
 #     cmake variables.
-#
-#   is_cross_compiling
-#     Whether this is cross-compiling host tools.
 macro(swift_common_standalone_build_config product)
   swift_common_standalone_build_config_llvm(${product})
-  swift_common_standalone_build_config_clang(${product})
-  swift_common_standalone_build_config_cmark(${product})
+  if(SWIFT_INCLUDE_TOOLS)
+    swift_common_standalone_build_config_clang(${product})
+    swift_common_standalone_build_config_cmark(${product})
+  endif()
 
   # Enable groups for IDE generators (Xcode and MSVC).
   set_property(GLOBAL PROPERTY USE_FOLDERS ON)