libdw: Make sure to get .eh_frame_hdr with .eh_frame in getcfi_shdr

libdw: Make sure to get .eh_frame_hdr with .eh_frame in getcfi_shdr

If we find a .eh_frame section we want to make sure to also get the
search table section .eh_frame_hdr. Otherwise lookups will be very
slow. Only create a Dwarf_CFI without a search table as a last resort.

	* libdw/dwarf_getcfi_elf.c (getcfi_shdr): Keep iterating
        through the shdrs till both .eh_frame and .eh_frame_hdr are
        found. Check both aren't SHT_NOBITS.

Suggested-by: Shimin Guo <shimin.guo@skydio.com>
Signed-off-by: Mark Wielaard <mark@klomp.org>