libelf: elf_compress doesn't handle multiple elf_newdata chunks correctly

libelf: elf_compress doesn't handle multiple elf_newdata chunks correctly

elf_compress would compress all (new) data chunks, but didn't reset
the section data_list. This would cause extra data to be returned
after decompression or create bad compressed data. Add a new testcase
for this and explicitly zap the scn->data_list before resetting the
elf section raw data after (de)compression.

	 * libelf/elf_compress.c (__libelf_reset_rawdata): Cleanup
         scn->data_list.
	 * tests/newzdata.c: New testcase.
	 * tests/Makefile.am (check_PROGRAMS): Add newzdata.
	 (TESTS): Likewise.
	 (newzdata_LDADD): New variable.

https://sourceware.org/bugzilla/show_bug.cgi?id=32102

Signed-off-by: Mark Wielaard <mark@klomp.org>