Small patch to regex_internal.h for z/OS

[Arnold Robbins]

Hi.

I have applied the following patch to my copy of regex_internal.h; it's
needed for compilation in the POSIX environment on z/OS.

Thanks,

Arnold
------------------------------
--- /usr/local/src/Gnu/gnulib/lib/regex_internal.h      2018-07-18 
21:16:31.670542200 +0300
+++ support/regex_internal.h    2018-08-22 18:46:06.006186098 +0300
@@ -149,7 +149,10 @@
 /* Rename to standard API for using out of glibc.  */
 #ifndef _LIBC
 # undef __wctype
+# undef __iswalnum
 # undef __iswctype
+# undef __towlower
+# undef __towupper
 # define __wctype wctype
 # define __iswalnum iswalnum
 # define __iswctype iswctype