[libcxx] locale.cpp: Move build_name helper into unnamed namespace (#92461)

Fix linkage of `build_name`; it is not supposed to have external
linkage.

Author: hubert-reinterpretcast

libcxx/src/locale.cpp

@@ -102,8 +102,6 @@ inline constexpr size_t countof(const T* const begin, const T* const end) {
   return static_cast<size_t>(end - begin);
 }
 
-} // namespace
-
 string build_name(const string& other, const string& one, locale::category c) {
   if (other == "*" || one == "*")
     return "*";
@@ -115,6 +113,8 @@ string build_name(const string& other, const string& one, locale::category c) {
   return "*";
 }
 
+} // namespace
+
 const locale::category locale::none;
 const locale::category locale::collate;
 const locale::category locale::ctype;