OBJCOPYFLAGS, READELF, READELFFLAGS, LD, LDFLAGS): Provide
default.
* lib/ld-lib.exp (run_dump_test): Import from gas testsuite. Add
new options "ld", "source", "xfail", "target", "notarget" and
"error". Support the runtest_file_p "*.exp=testname" feature.
(slurp_options, regexp_diff, file_contents, verbose_eval): Import
from gas testsuite.