INSTALL: fix compiler detection on FreeBSD+clang (#177)

INSTALL

@@ -42,10 +42,14 @@ echo "* Resetting $PLAN9/config"
 rm -f config
 
 (
-echo "* Compiler version:"
-9c -v 2>&1 | grep -v 'Configured with:' | grep -i version | sed 's/^/	/'
-
 if [ `uname` = FreeBSD ]; then
+	case `cc -v 2>&1` in
+	*clang*)
+		echo "CC9=clang" >> $PLAN9/config
+		;;
+	*)
+		;;
+	esac
 	echo "* Running on FreeBSD, adjusting linker flags"
 	echo "LDFLAGS='-L/usr/local/lib'" >> $PLAN9/config
 fi
@@ -147,6 +151,9 @@ if [ -f LOCAL.config ]; then
 	cat LOCAL.config >>config
 fi
 
+echo "* Compiler version:"
+9c -v 2>&1 | grep -v 'Configured with:' | grep -i version | sed 's/^/	/'
+
 cd src
 if $dobuild; then
 	if [ ! -x ../bin/mk ]; then