Hello guix,

I find out that there are a lof of erroneous uses of regex in the
invokation of FIND-FILES. The correct usage should be:

  (find-files "." "\\.c$")

Instead people write:

  (find-files "." ".*\\.c")

which match unwanted files.

For examples, in the procedure CUSTOM-GCC, the correct regex should be:

  "(c\\+\\+|cpp|g\\+\\+|gcov|gcc|gcc-.*)$"

instead of:

  ".*(c\\+\\+|cpp|g\\+\\+|gcov|gcc|gcc-.*)"

Please correct me if I am wrong.

Right now, the erroneous use of regex in CUSTOM-GCC casues the 'bin/'
directory of the output of gccgo, gcc-objc and gcc-objc++ to be empty.