PR25191, internal error in _bfd_elf_set_section_contents

PR25191, internal error in _bfd_elf_set_section_contents

This PR copies a fuzzed PE input file to ELF output, in the process
confusing the ELF backend by copying COFF-only section flags to the
output.  SEC_COFF_SHARED has the same value as SEC_ELF_COMPRESS.  One
approach to fixing this problem is of course not to reuse flag bits,
but we've run out.  So this patch only copies section flags that are
in the bfd_applicable_section_flags set when changing the flavour of
the output file.

	PR 25191
	* objcopy.c (is_nondebug_keep_contents_section): Use bfd_get_flavour.
	(copy_object): Likewise.
	(setup_section): Likewise.  If flavour of input and output files
	differ, restrict section flags to the intersection of input and
	output bfd_applicable_section_flags.