LibC: Don't include things required for getopt_long in unistd.h

Previously, we were including the whole of <getopt.h> in <unistd.h>.
However according to the posix <unistd.h> doesn't have to contain
everything we had in <getopt.h>.

This fixes some symbol collisions that broke the git port.

Libraries/LibC/unistd.cpp

@@ -32,6 +32,7 @@
 #include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
+#include <getopt.h>
 #include <grp.h>
 #include <pwd.h>
 #include <stdarg.h>