elflint: Add gnuld check when a NOBITS section falls inside a segment.

elflint: Add gnuld check when a NOBITS section falls inside a segment.

gnuld has a really bad bug where it can place a NOBITS section inside
a PT_LOAD segment. Normally that would not work. But it also makes sure
that the contents of the file is all zeros. So in practice it is actually
a PROGBITS section with all zero data. Except that other tools will think
there is an unused gap in the ELF file after the NOBITS section.

Recognize and check this pattern in elflint when --gnu is given.

Signed-off-by: Mark Wielaard <mjw@redhat.com>