I wrongly thought the option is for extracting names of commit authors to
changelog subtitles. But gbp(1) already does it automatically.

 * At Matthias Klose's request, removed auto-tests with fixed versions of GCC
   or Clang. Instead, use default compilers.
 * Rewritten the tests so that they include system-wide installed GSL headers.

Closes: #976037

Closes: #972944

CTest can not use Make's jobserver and awaits peculiarly passed ARGS to
do parallel testing. On my laptop, the test stage takes 17 seconds for
some reason, although on Salsa CI it takes less than a second. Alas, I
do not know what causes such discrepancy. However, this change speeds up
for me four-threaded test running by about 2 minutes.

 * Remove no longer needed CMAKE_SKIP_INSTALL_ALL_DEPENDENCY variable.

Closes: #966895

Fixes lintian: upstream-metadata-file-is-missing
See https://lintian.debian.org/tags/upstream-metadata-file-is-missing.html for more details.

Update to upstream version '3.1.0'
with Debian dir 413ba5db002caa76081f7a3e74b001fe7c2a4c00

Update to upstream version '3.0.1'
with Debian dir f893a39552e70d55b47687699ab672e951a8ad70

Update to upstream version '3.0.0'
with Debian dir cc6a20aa7edce778b78265e5dd80e73b698c5f34

 * Use debhelper compatibility level 12.
 * Specify minimal required CMake version 3.1.3.

Update to upstream version '2.1.0'
with Debian dir 363d26b5a59e2d30c2a82c8a56ee62146372a0a1

Closes: #906385

 * Lintian requires that timestamp of the last entry in the d/changelog
   would be later than time of the Debian policy release.

 * There were significant changes in the package meta information.
   - New implementation of the nochek build profile in d/rules.
   - New d/gbp.conf file to reflect upstream versions.
   - New d/watch file for uscan(1).