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/stdio/unlocked.h

@@ -4,6 +4,9 @@
 #if !(__ASSEMBLER__ + __LINKER__ + 0)
 COSMOPOLITAN_C_START_
 
+void flockfile(FILE *);
+void funlockfile(FILE *);
+int ftrylockfile(FILE *);
 int getc_unlocked(FILE *) paramsnonnull();
 int getchar_unlocked(void);
 int putc_unlocked(int, FILE *) paramsnonnull();