posix_getgrnam returns false when no group gound

Summary: getgrnam_r and getgrgid_r return zero on success and an error number on failure.
If no matching group was found they return 0 and store NULL in *result.

This fixes three zend tests. Two of them have the exact same content though (lol)
Closes https://github.com/facebook/hhvm/pull/3722

Reviewed By: @fredemmott

Differential Revision: D1548070
Reorganize some TARGETs files to avoid "../" warnings

Summary: Just a bit of cleanup. Removes all the .cpp related warnings
from fbconfig -r hphp.

Reviewed By: @edwinsmith

Differential Revision: D1556540
Fix gmp_strval base issue

Summary: We were using the supplied input base value meant for output on the input, causing bad mojo.  This fixes it to only use the base for creating the output string.

Fixes #3793
Closes https://github.com/facebook/hhvm/pull/3794

Reviewed By: @fredemmott

Differential Revision: D1566171