This is necessary when building a gnu cross compiler for a musl target.
Otherwise, even if clocale manually is set to gnu, it will be reset to generic
when the test is performed using AC_EGREP_CPP().
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -16694,6 +16694,7 @@ fi
 
   # Sanity check model, and test for special functionality.
   if test $enable_clocale_flag = gnu; then
+    if test $enable_clocale = auto; then
     cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
 
@@ -16710,6 +16711,7 @@ else
   enable_clocale_flag=generic
 fi
 rm -f conftest*
+    fi
 
 
     # Set it to scream when it hurts.
