tools/ccsym: update for modern versions of gcc

This dumps the predefined preprocessor macros

src/tools/ccsym

@@ -1,16 +1,4 @@
 #!/bin/sh
 
-# src/tools/ccsym
-
-trap "rm -f /tmp/$$.*" 0 1 2 3 15
-cd /tmp
-cat >$$.c <<EOF
-extern int foo;
-EOF
-for i in `cc -v -c $$.c 2>&1`
-do
-        case "$i" in
-        -D*) echo "$i" | sed 's/^-D//';;
-        -A*) echo "$i" | sed 's/^-A\(.*\)(\(.*\))/\1=\2/';;
-        esac
-done
+# display gcc predefined preprocessor macros
+gcc -dM -E - < /dev/null