Use nl_langinfo_l with an explicitly created locale

(where empty string arg to newlocale, per SUSv4, means "an implementation-
defined native environment.  This correspons to the value of the associated
environment variables, LC_* and LANG") instead of relying on whatever setlocale
would be in effect here.

Also, nl_langinfo_l is less of an MT nightmare than nl_langinfo, which is of
benefit once the last remaining use of nl_langinfo in sal/osl/unx/nlsupport.cxx
will also have been changed to nl_langinfo_l.

loplugin:nullptr needs a little hack, as SUSv4 locale_t could be anything from
an integer type to a pointer type.

Change-Id: Ic35dcbc2e0a4f650694b48df12470dd89476dff5

compilerplugins/clang/nullptr.cxx

@@ -12,6 +12,7 @@
 #include <limits>
 #include <set>
 
+#include "check.hxx"
 #include "plugin.hxx"
 
 namespace {
@@ -128,6 +129,11 @@ bool Nullptr::VisitImplicitCastExpr(CastExpr const * expr) {
     case Expr::NPCK_CXX11_nullptr:
         break;
     default:
+        if (loplugin::TypeCheck(expr->getType()).Typedef("locale_t")
+            .GlobalNamespace())
+        {
+            break; // POSIX locale_t is left unspecified
+        }
         handleNull(expr->getSubExpr(), expr->getCastKindName(), k);
         break;
     }