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

tool/emacs/cosmo-c-constants.el

@@ -37,6 +37,7 @@
     "SIZEOF_FLOAT80"
     "SIZEOF_LONG_DOUBLE"
     "SIZEOF_INTMAX"
+    "CHAR_MAX"
     "SCHAR_MAX"
     "SHRT_MAX"
     "INT_MAX"