Add debuginfod support to GDB

debuginfod is a lightweight web service that indexes ELF/DWARF debugging
resources by build-id and serves them over HTTP.

This patch enables GDB to query debuginfod servers for separate debug
files and source code when it is otherwise not able to find them.

GDB can be built with debuginfod using the --with-debuginfod configure
option.

This requires that libdebuginfod be installed and found at configure time.

debuginfod is packaged with elfutils, starting with version 0.178.

For more information see https://sourceware.org/elfutils/.

Tested on x86_64 Fedora 31.

gdb/ChangeLog:
2020-02-26  Aaron Merey  <amerey@redhat.com>

        * Makefile.in: Handle optional debuginfod support.
        * NEWS: Update.
        * README: Add --with-debuginfod summary.
        * config.in: Regenerate.
        * configure: Regenerate.
        * configure.ac: Handle optional debuginfod support.
        * debuginfod-support.c: debuginfod helper functions.
        * debuginfod-support.h: Ditto.
        * doc/gdb.texinfo: Add --with-debuginfod to configure options
        summary.
        * dwarf2/read.c (dwarf2_get_dwz_file): Query debuginfod servers
        when a dwz file cannot be found.
        * elfread.c (elf_symfile_read): Query debuginfod servers when a
        debuginfo file cannot be found.
        * source.c (open_source_file): Query debuginfod servers when a
        source file cannot be found.
        * top.c (print_gdb_configuration): Include
        --{with,without}-debuginfod in the output.

gdb/testsuite/ChangeLog:
2020-02-26  Aaron Merey  <amerey@redhat.com>

        * gdb.debuginfod: New directory for debuginfod tests.
        * gdb.debuginfod/main.c: New test file.
        * gdb.debuginfod/fetch_src_and_symbols.exp: New tests.

1 files changed, 9 insertions, 0 deletions

diff --git a/gdb/README b/gdb/README
index 3895758ece5..0ec1605ce5a 100644
--- a/gdb/README
+++ b/gdb/README
@@ -432,6 +432,15 @@ more obscure GDB `configure' options are not listed here.
      Use the curses library instead of the termcap library, for
      text-mode terminal operations.
 
+`--with-debuginfod'
+     Build GDB with libdebuginfod, the debuginfod client library.  Used
+     to automatically fetch source files and separate debug files from
+     debuginfod servers using the associated executable's build ID.
+     Enabled by default if libdebuginfod is installed and found at
+     configure time.  debuginfod is packaged with elfutils, starting
+     with version 0.178.  You can get the latest version from
+     'https://sourceware.org/elfutils/'.
+
 `--with-libunwind-ia64'
      Use the libunwind library for unwinding function call stack on ia64
      target platforms.