* objcopy.c (copy_main): Rewrite OPTION_ADD_SECTION code to work
with non-ordinary files like /dev/null.
binutils/testsuite/:
* lib/utils-lib.exp (run_dump_test): Permit option values to use
$srcdir to refer to the source directory.
* binutils-all/add-section.d: New test.
* binutils-all/add-empty-section.d: New test.
* binutils-all/empty-file: New test input file.
* binutils-all/objcopy.exp: Run new tests.
