when on windows *and* ecl, use the value of c:*cc* as the c copmiler as opposed to assuming the hardcoded msys path.
use ext:run-program on ecl/windows

this is to fix an "input line is too long" error when compiling files
with longer names. it's important to note that this has very similar
behavior to ext:system. it returns the status code on exit, and throws
an error when the command fails for whatever reason.