test-lib: add GIT_SAN_OPTIONS, inherit [AL]SAN_OPTIONS
Change our ASAN_OPTIONS and LSAN_OPTIONS to set defaults for those variables, rather than punting out entirely if we already have them in the environment. We want to take any user-provided settings over our own, but we can do that by prepending our defaults to the variable. The libsanitizer options parsing has "last option wins" semantics. It's now possible to do e.g.: LSAN_OPTIONS=report_objects=1 ./t0006-date.sh And not have the "report_objects=1" setting overwrite our sensible default of "abort_on_error=1", but by prepending to the list we ensure that: LSAN_OPTIONS=report_objects=1:abort_on_error=0 ./t0006-date.sh Will take the desired "abort_on_error=0" over our default. See b0f4c9087e1 (t: support clang/gcc AddressSanitizer, 2014-12-08) for the original pattern being altered here, and 85b81b35ff9 (test-lib: set LSAN_OPTIONS to abort by default, 2017-09-05) for when LSAN_OPTIONS was added in addition to the then-existing ASAN_OPTIONS. Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>