Add a mandatory debuginfod_begin()/_end() call pair to manage a client
object that represents persistent but non-global state.  From libdwfl,
dlopen the debuginfod.so client library early on.  This hopefully
makes sure that the code (and the libcurl.so dependency) is loaded
before the program goes into multi-threaded mode.

Signed-off-by: Mark Wielaard <mark@klomp.org>

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>
Signed-off-by: Mark Wielaard <mark@klomp.org>
Signed-off-by: Aaron Merey <amerey@redhat.com>

This webapi extensions allows admins to hook up debuginfod to a
prometheus-compatible monitoring system for general situational
statistics.  The metrics are simple enough that local curl requests
can give a user a sense of what's going on.  The metrics are
documented as unstable with respect to future versions.

In order to support file/rpm archives that are organized via symlink
trees, add an "-L" option to debuginfod, meaning about the same as for
find(1) or ls(1): to traverse rather than ignore symlinks.

For interactive clients such as gdb, interruptibility is important for
usability during longer downloads.  This patchset adds a
download-progress callback function to the debuginfod client library,
with which a caller app can interrupt a download as well as be
notified of its quantitative progress.

Add the server to the debuginfod/ subdirectory.  This is a highly
multithreaded c++11 program (still buildable on rhel7's gcc 4.8,
which is only partly c++11 compliant).  Includes an initial suite
of tests, man pages, and a sample systemd service.

Signed-off-by: Frank Ch. Eigler <fche@redhat.com>
Signed-off-by: Aaron Merey <amerey@redhat.com>

Introduce the debuginfod/ subdirectory, containing the client for a
new debuginfo-over-http service, in shared-library and command-line
forms.  Two functions in libdwfl make calls into the client library to
fetch elf/dwarf files by buildid, as a fallback.  Instead of normal
dynamic linking (thus pulling in a variety of curl dependencies),
the libdwfl hooks use dlopen/dlsym.  Server & tests coming in patch 2.

Signed-off-by: Aaron Merey <amerey@redhat.com>
Signed-off-by: Frank Ch. Eigler <fche@redhat.com>