Removing gnu99 constructs from elfutils

[Timm Bäder]

Hi,

I'm looking into removing both the nested functions as well as
variable-length arrays in the elfutils source code, so it can be built
using clang. This is a continuation of
https://sourceware.org/bugzilla/show_bug.cgi?id=24964 basically.

I did try to incorporate some cleanup commits as well so the result does
not get too ugly. Some of the nested functions have quite a few hidden
dependencies on the surrounding code.

I started with libdwfl/dwfl_segment_report_module.c but am planning on
converting everything else as well of course.

What do you think?


Thanks,
Timm