cc-wrapper: Don't treat "-" alone as a flag

It means stdin, and is morally equivalent to passing a file. e.g.

  $ echo 'int main(void) { return 0; }' | gcc -x c -

will compile and link a binary.

pkgs/build-support/cc-wrapper/cc-wrapper.sh

@@ -59,7 +59,8 @@ while (( "$n" < "$nParams" )); do
         cppInclude=0
     elif [ "$p" = -nostdinc++ ]; then
         cppInclude=0
-    elif [ "${p:0:1}" != - ]; then
+    elif [[ "$p" != -?* ]]; then
+        # A dash alone signifies standard input; it is not a flag
         nonFlagArgs=1
     fi
     n+=1