Fix ISO C++11 -Wwritable-strings

osl/unx/nlsupport.cxx:863:18: warning: ISO C++11 does not allow \
  conversion from string literal to 'char *' [-Wwritable-strings]

Change-Id: I45da986ad8992716df9d1f9a0cc443fdb9cd46ba
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/128213
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

sal/osl/unx/nlsupport.cxx

@@ -848,10 +848,10 @@ void imp_getProcessLocale( rtl_Locale ** ppLocale )
     /* No locale environment variables on Android, so why even bother
      * with getenv().
      */
-   char const * locale = "en-US.UTF-8";
+    const char* locale = "en-US.UTF-8";
 #else
     /* simulate behavior off setlocale */
-    char * locale = getenv( "LC_ALL" );
+    const char* locale = getenv("LC_ALL");
 
     if( NULL == locale )
         locale = getenv( "LC_CTYPE" );