Merge branch 'jk/build-with-asan'

The build procedure has been improved to allow building and testing Git with address sanitizer more easily. * jk/build-with-asan: Makefile: disable unaligned loads with UBSan Makefile: turn off -fomit-frame-pointer with sanitizers Makefile: add helper for compiling with -fsanitize test-lib: turn on ASan abort_on_error by default test-lib: set ASAN_OPTIONS variable before we run git