Also find CFI in sections of type SHT_X86_64_UNWIND
On my system with g++ (GCC) 8.2.1
20180831 with GNU gold (GNU Binutils
2.31.1) 1.16, the .eh_frame section does not have type PROGBITS
but rather is using X86_64_UNWIND nowadays:
```
$ echo "int main(){ return 0; }" > test.c
$ gcc test.c
$ readelf --sections a.out | grep .eh_frame
[14] .eh_frame X86_64_UNWIND
0000000000000670 00000670
[15] .eh_frame_hdr X86_64_UNWIND
0000000000000724 00000724
```
Without this patch, libdw refuses to use the available unwind
information, leading to broken backtraces while unwinding. With the
patch applied, unwinding works once more in such situations.
Signed-off-by: Milian Wolff <milian.wolff@kdab.com>
Signed-off-by: Mark Wielaard <mark@klomp.org>
Tested-by: Milian Wolff <milian.wolff@kdab.com>