It is useful to look at the testsuite log file for information about how the tests were run. For example, which compiler was used, and with what compiler options. We need to balance this against providing information which will always change, making diffs hard to read.
The most extreme case would be to output all make variables. Maybe better would be to output CC, CFLAGS, CXX, etc. Another option would be to parse these and say "intel compiler", "gcc", "pgi" etc.