[perl #59980] [CAGE] 'make' warnings

[chromatic via RT]

We can't solve all of those warnings (the GDBM aggregate warnings are
exceedingly stupid, from the dark ages of pre-ANSI C compilers, and some
of the IMCC errors are due to generated code from flex and bison that
we'll never fix unless we post-process generated code, which we aren't
going to do to fix warnings), but I've done what we can do in r32748,
which should suffice for now.