consolidate str[n]casecmp_l into str[n]casecmp source files

this is mainly done for consistency with the ctype functions and to
declutter the src/locale directory.

src/locale/strcasecmp_l.c

-#include <strings.h>
-
-int strcasecmp_l(const char *l, const char *r, locale_t loc)
-{
-	return strcasecmp(l, r);
-}

src/locale/strncasecmp_l.c

-#include <strings.h>
-#include <locale.h>
-
-int strncasecmp_l(const char *l, const char *r, size_t n, locale_t loc)
-{
-	return strncasecmp(l, r, n);
-}

src/string/strcasecmp.c

 #include <strings.h>
 #include <ctype.h>
+#include "libc.h"
 
 int strcasecmp(const char *_l, const char *_r)
 {
@@ -7,3 +8,10 @@ int strcasecmp(const char *_l, const char *_r)
 	for (; *l && *r && (*l == *r || tolower(*l) == tolower(*r)); l++, r++);
 	return tolower(*l) - tolower(*r);
 }
+
+int __strcasecmp_l(const char *l, const char *r, locale_t loc)
+{
+	return strcasecmp(l, r);
+}
+
+weak_alias(__strcasecmp_l, strcasecmp_l);

src/string/strncasecmp.c

 #include <strings.h>
 #include <ctype.h>
+#include "libc.h"
 
 int strncasecmp(const char *_l, const char *_r, size_t n)
 {
@@ -8,3 +9,10 @@ int strncasecmp(const char *_l, const char *_r, size_t n)
 	for (; *l && *r && n && (*l == *r || tolower(*l) == tolower(*r)); l++, r++, n--);
 	return tolower(*l) - tolower(*r);
 }
+
+int __strncasecmp_l(const char *l, const char *r, size_t n, locale_t loc)
+{
+	return strncasecmp(l, r, n);
+}
+
+weak_alias(__strncasecmp_l, strncasecmp_l);