Remove unneeded and sometimes missing headers.

diff -ur ld64-241.9/src/ld/Options.cpp work/ld64-241.9/src/ld/Options.cpp
--- ld64-241.9/src/ld/Options.cpp	2015-01-22 21:42:04.000000000 +0100
+++ ld64-241.9/src/ld/Options.cpp	2015-01-22 21:45:15.000000000 +0100
@@ -31,7 +31,6 @@
 #include <fcntl.h>
 #include <errno.h>
 #include <string.h>
-#include <spawn.h>
 #include <cxxabi.h>
 #include <Availability.h>