configure: Allow user override LD, AR, OBJCOPY, and GPROF

configure: Allow user override LD, AR, OBJCOPY, and GPROF

The only way to override LD, AR, OBJCOPY, and GPROF is through
--with-binutils (setting the environments variables on configure is
overridden by LIBC_PROG_BINUTILS).

The build-many-glibcs.py (bmg) glibcs option generates a working config,
but not fully concise (some tools will be set from environment variable,
while other will be set from $CC --print-prog-name).  So remove the
environment variable set to always use the "$CC --print-prog-name".
Reviewed-by: Carlos O'Donell <carlos@redhat.com>