diff -ruN gildas-src-jun18a/admin/define-system.sh gildas-src-jun18a.clang/admin/define-system.sh
--- gildas-src-jun18a/admin/define-system.sh	2018-03-12 11:07:57.000000000 +0100
+++ gildas-src-jun18a.clang/admin/define-system.sh	2018-06-12 14:56:14.000000000 +0200
@@ -218,13 +218,13 @@
         	else
         	    GAG_MACHINE=pc
         	fi
-                if which gcc > /dev/null 2>&1; then
-                    DEFAULT_CCOMPILER=gcc
+                if which clang > /dev/null 2>&1; then
+                    DEFAULT_CCOMPILER=clang
                 fi
-                if which g++ > /dev/null 2>&1; then
-                    DEFAULT_CXXCOMPILER=g++
-                elif which clang++ > /dev/null 2>&1; then
+                if which clang++ > /dev/null 2>&1; then
                     DEFAULT_CXXCOMPILER=clang++
+                elif which g++ > /dev/null 2>&1; then
+                    DEFAULT_CXXCOMPILER=g++
                 fi
         	if which ifort > /dev/null 2>&1; then
         	    DEFAULT_FCOMPILER=ifort