Fix incremental tests using gcc 9, which adds Gnu properties sections.

Fix incremental tests using gcc 9, which adds Gnu properties sections.

During an incremental link, we should simply ignore the Gnu properties
sections. We were not handling them properly -- failing to process the
properties from the base file. While that could be fixed, the property
sections are meant for deployed binaries, and incremental linking is
for development, so keeping the properties sections just adds to the
likelihood of forcing a full link sooner.

gold/
	PR gold/23539
	* object.cc (Sized_relobj_file::layout_gnu_property_section): Ignore
	Gnu properties during incremental links.