tools: Portability fix for gpgparsemail.

* tools/rfc822parse.c (my_stpcpy): Rename from stpcpy.

--

When HAVE_STPCPY is not defined (no definition in libc), still,
compiler may have definition as a built-in function (for some specific
case like second argument is constant).  In that case, having stpcpy
implementation with the same name but different signature ("static"
qualifier) is not good.

Signed-off-by: NIIBE Yutaka <gniibe@fsij.org>

tools/rfc822parse.c

@@ -155,7 +155,7 @@ capitalize_header_name (unsigned char *name)
 
 #ifndef HAVE_STPCPY
 static char *
-stpcpy (char *a,const char *b)
+my_stpcpy (char *a,const char *b)
 {
   while (*b)
     *a++ = *b++;
@@ -163,6 +163,7 @@ stpcpy (char *a,const char *b)
 
   return (char*)a;
 }
+#define stpcpy my_stpcpy
 #endif