libdwfl: Check for kernel debuginfo file without .debug extension as well

libdwfl: Check for kernel debuginfo file without .debug extension as well

Elfutils, looking for kernel debuginfo file, tries to find it at
various places. If elfutils finds /boot/vmlinu*x* file, it checks
for debufginfo section. If debuginfo is not present, it saves it as
'main elf' and continue looking for debuginfo file having .debug
extension i.e. vmlinux-RELEASE.debug.

'Ubuntu on powerpc' installs kernel as /boot/vmlinux and installs
debuginfo without any extension as /usr/lib/debug/boot/vmlinux-RELEASE
and hence, elfutils is not able to find the debuginfo file.

Here is the launchpad bug for the same:
  https://bugs.launchpad.net/ubuntu/+source/systemtap/+bug/1537125

This patch adds functionality to search for a kernel or debuginfo file
both with and without .debug extension.

Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.vnet.ibm.com>
Signed-off-by: Mark Wielaard <mjw@redhat.com>