build: quote library search path options

When passing the linker search path options to the driver, ensure that
we quote the argument.  We would previously incorrectly split the
arguments that were passed to the driver if there were spaces.  This
would manifest as link failures on Linux when cross-compiling to
Windows.

Author: compnerd

cmake/modules/AddSwift.cmake

@@ -497,7 +497,7 @@ endfunction()
 function(swift_target_link_search_directories target directories)
   set(STLD_FLAGS "")
   foreach(directory ${directories})
-    set(STLD_FLAGS "${STLD_FLAGS} ${CMAKE_LIBRARY_PATH_FLAG}${directory}")
+    set(STLD_FLAGS "${STLD_FLAGS} \"${CMAKE_LIBRARY_PATH_FLAG}${directory}\"")
   endforeach()
   set_property(TARGET ${target} APPEND_STRING PROPERTY LINK_FLAGS ${STLD_FLAGS})
 endfunction()