LibC: Implement getopt_long{,_only}

Few ports attempt to use this so lets add them :D

userspace/libraries/LibC/CMakeLists.txt

@@ -12,6 +12,7 @@ set(LIBC_SOURCES
 	fenv.cpp
 	fnmatch.cpp
 	ftw.cpp
+	getopt.cpp
 	grp.cpp
 	ifaddrs.cpp
 	inttypes.cpp