Remove -stdlib=libc++ flag on Mac

This is the default since Mac OS 10.9 and we don't support any
versions older than that. In newer versions of Clang, it causes
warning spam about an unused flag so remove it.

Author: slipher

cmake/DaemonFlags.cmake

@@ -262,10 +262,6 @@ else()
 		# PNaCl only supports libc++ as standard library.
 		set_c_cxx_flag("-stdlib=libc++")
 		set_c_cxx_flag("--pnacl-allow-exceptions")
-	elseif (APPLE)
-		# Use libc++ on Mac because the shipped libstdc++ version is too old.
-		set_c_cxx_flag("-stdlib=libc++")
-		set_linker_flag("-stdlib=libc++")
 	endif()
 
 	# Prevent the generation of STB_GNU_UNIQUE symbols