Include relevant env vars on command line.

Makes it easier to reproduce a build by cut/pasting the configure line.

.github/configure.sh

@@ -2,5 +2,20 @@
 
 . .github/configs $1
 
-set -x
+printf "$ "
+
+if [ "x$CC" != "x" ]; then
+	printf "CC='$CC' "
+fi
+if [ "x$CFLAGS" != "x" ]; then
+	printf "CFLAGS='$CFLAGS' "
+fi
+if [ "x$CPPFLAGS" != "x" ]; then
+	printf "CPPFLAGS='$CPPFLAGS' "
+fi
+if [ "x$LDFLAGS" != "x" ]; then
+	printf "LDFLAGS='$LDFLAGS' "
+fi
+
+echo ./configure ${CONFIGFLAGS}
 ./configure ${CONFIGFLAGS}