Add more POSIX function stubs

Cosmopolitan currently doesn't support threads and it doesn't do
anything fancy in longjmp/setjmp so this change was simple to do

- localeconv
- _setjmp (same as setjmp)
- _longjmp (same as longjmp)
- strcoll (same as strcmp)
- flockfile (does nothing)
- funlockfile (does nothing)
- ftrylockfile (does nothing)

See #61

libc/runtime/runtime.h

@@ -39,6 +39,8 @@ unsigned long getauxval(unsigned long);
 void *mapanon(size_t) vallocesque attributeallocsize((1));
 int setjmp(jmp_buf) libcesque returnstwice paramsnonnull();
 void longjmp(jmp_buf, int) libcesque wontreturn paramsnonnull();
+int _setjmp(jmp_buf) libcesque returnstwice paramsnonnull();
+void _longjmp(jmp_buf, int) libcesque wontreturn paramsnonnull();
 void exit(int) wontreturn;
 void _exit(int) libcesque wontreturn;
 void _Exit(int) libcesque wontreturn;