Fixes for ECL on Windows using MinGW

The packaged commits do the following

- Fix a path assumption for the value of `*cc*` in grovel.lisp. When on Windows/ECL/(NOT cygwin), use the value of ECL's `c:*cc*` as the compiler instead of hardcoding the `c:/msys/1.0/bin/gcc.exe` path.
- Fix an error when compiling with ECL: "Input line is too long." This happens when compiling with lots of flags and long filenames. The fix is to use `ext:run-program` directly and match its arguments to the ones the `ext:system` uses internally, also returning the return code from the operation.

Thanks!