Fix compile errors, code review feedback, and add basic libc test suite.

@@ -70,13 +70,13 @@
                 errno = EINVAL;
                 return (NULL);
         }
 
         if (locname == NULL)
-                return (current_locale(__global_locale, category));
+                return (current_locale(___global_locale, category));
 
-        if ((oldloc = duplocale(__global_locale)) == NULL)
+        if ((oldloc = duplocale(___global_locale)) == NULL)
                 return (NULL);
 
         mask = (category == LC_ALL ? LC_ALL_MASK : (1 << category));
 
         newloc = newlocale(mask, locname, oldloc);

@@ -83,12 +83,12 @@
         if (newloc == NULL) {
                 freelocale(oldloc);
                 return (NULL);
         }
 
-        oldloc = __global_locale;
-        __global_locale = newloc;
+        oldloc = ___global_locale;
+        ___global_locale = newloc;
 
         install_legacy(newloc, mask);
 
         freelocale(oldloc);
         return (current_locale(newloc, category));