There are compilers other than Visual C that want to show absolute
paths. Generalize the helper introduced by a2c5e294 (unit-tests: do
show relative file paths, 2023-09-25) so that it can also work with
a path that uses slash as the directory separator, and becomes
almost no-op once one-time preparation finds out that we are using a
compiler that already gives relative paths. Incidentally, this also
should do the right thing on Windows with a compiler that shows
relative paths but with backslash as the directory separator (if
such a thing exists and is used to build git).
Reported-by: Randall S. Becker <rsbecker@nexbridge.com>
Helped-by: Phillip Wood <phillip.wood@dunelm.org.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
f66286364f