add internal header for declaring __pleval function (used by gettext)

locale_impl.h could have been used, but this function is completely
independent of anything else, and preserving that property seems nice.

src/locale/dcngettext.c

@@ -8,6 +8,7 @@
 #include "locale_impl.h"
 #include "libc.h"
 #include "atomic.h"
+#include "pleval.h"
 
 struct binding {
 	struct binding *next;
@@ -114,7 +115,6 @@ weak_alias(dummy_gettextdomain, __gettextdomain);
 
 const unsigned char *__map_file(const char *, size_t *);
 int __munmap(void *, size_t);
-unsigned long __pleval(const char *, unsigned long);
 
 char *dcngettext(const char *domainname, const char *msgid1, const char *msgid2, unsigned long int n, int category)
 {

src/locale/pleval.c

 #include <stdlib.h>
 #include <ctype.h>
+#include "pleval.h"
 
 /*
 grammar:

src/locale/pleval.h

+#ifndef PLEVAL_H
+#define PLEVAL_H
+
+unsigned long __pleval(const char *, unsigned long);
+
+#endif