Fix regex wctype namespace (bug 18495).

Fix regex wctype namespace (bug 18495).

regcomp brings in references to various wctype functions that aren't
in all the standards including regcomp.  This patch fixes this in the
usual way by using the __* versions of these functions (which already
exist, but some didn't have libc_hidden_proto / libc_hidden_def
before).

Tested for x86_64 and x86 (testsuite, and that installed stripped
shared libraries are unchanged by the patch).  (Other wide character
function references from the regex code mean that this patch by itself
doesn't fix any XFAILed linknamespace test failures; further patches
will be needed for that.)

	[BZ #18495]
	* wctype/wcfuncs.c (__iswalnum): Use libc_hidden_def.
	(__iswlower): Likewise.
	* include/wctype.h (__iswalnum): Declare.  Use libc_hidden_proto.
	(__iswlower): Likewise.
	* posix/regcomp.c (re_compile_fastmap_iter): Call __towlower
	instead of towlower.
	* posix/regex_internal.c (build_wcs_upper_buffer): Call __iswlower
	instead of iswlower.  Call __towupper instead of towupper.
	* posix/regex_internal.h (IS_WIDE_WORD_CHAR): Call __iswalnum
	instead of iswalnum.