build bootstrap 'GITIGNOREFILES'

[kgold2]

Ubuntu 16 and 20, latest master (I think), bootstrap gives this error:

Generating file lists: src_vars.mk
aminclude_static.am:63: warning: GITIGNOREFILES was already defined in condition TRUE, which includes condition AUTOCONF_CODE_COVERAGE_2019_01_06 and CODE_COVERAGE_ENABLED ...
Makefile.am:56: 'aminclude_static.am' included from here
Makefile.am:52: ... 'GITIGNOREFILES' previously defined here

[tstruk]

As explained on the mailing list - this is because the code coverage macros from the autoconf-archive changed in a way that breaks backward compatibility. We have put a workaround to support both the old version as well as the new one as a temporary solution, but the downside is that it generates this warning.
We can fix the warning and switch to the new version completely, but this will make the build fail on old systems (ubuntu 16.04)