bug#19733: disfunctional gcc binary when GCJ or gfortran is installed

[Ricardo Wurmus]

Commit 5f6887e8 fixes this for GCJ, but we still have this problem for
all variants of gfortran, gcc-objc, and gccgo, all of which are built
using the ‘custom-gcc’ procedure.

It’s probably safe to add a build phase like this to ‘custom-gcc’:

    (add-after 'install 'remove-broken-or-conflicting-files
     (lambda* (#:key outputs #:allow-other-keys)
       (for-each delete-file
         (find-files (string-append (assoc-ref outputs "out") "/bin")
                     ".*(c\\+\\+|cpp|g\\+\\+|gcc.*)"))
       #t))

~~ Ricardo