Hello,

[GNU-796] Stabilize GDB testsuite results in the CI:

- Moved most of logic to rerun failed tests from tcwg_gnu-build.sh to Abe and a new script based on the sum file parser of compare_dg_tests.pl. The new script creates a "merged" sum file from all the runs. Currently changing Abe to make use of it.

- Did a few cleanups in compare_dg_tests.pl as I was going through its code. Also added KFAIL status support to it, which the GDB testsuite needs.

- Removed a few obsolete CI jobs which came out of the woodwork when I merged the compare_dg_tests.pl cleanups.