regex no longer needs to depend on malloc-gnu

[Nathan Kennedy]

The malloc-gnu (then malloc) dependency was added at 
91f0c71300fb4f48cd39df121b8434f56012502c in response to a bug report 
with sed built against uClibc: 
http://lists.gnu.org/archive/html/bug-gnu-utils/2005-08/msg00112.html

The error was directly fixed at bbf0d723ed2335add96bcc0f842885d8a5d8b6da 
so I think this dependency can be removed.

Also, I filed bug 16851 against glibc/regex to get the bbf0d72... fix in 
glibc.  For the sake of glibc/gnulib regex harmonization, I also 
observed that the MALLOC_0_IS_NONNULL macro attempting to check for 
malloc(0) failure is not needed. It should be enough to add "&& size != 0".

Best,
Nathan