meson: fix MERGE_TOOL_DIR with "--no-bin-wrappers"

On Windows, we execute tests with "--no-bin-wrappers". This has been
introduced via a87e427e35 (ci: speed up Windows phase, 2019-01-29) to
save some time: spawning processes is expensive on Windows, and shell
scripts tend to spawn a bunch of them. So overall, the bin-wrappers led
to a performance overhead of ~10-30%.

This causes test failures when using Meson on Windows:

  failure: t7610.28 mergetool --tool-help shows recognized tools
    ++ git mergetool --tool-help
    /d/a/git/git/build/git-mergetool--lib: line 45: cd: D:/a/git/git/build/mergetools: No such file or directory

The root cause here is that our bin-wrappers are usually responsible for
setting up the `MERGE_TOOL_DIR` environment variable so that we can
locate these scripts. But as we don't use the bin-wrappers, we'll
instead use the default location for merge tools, which is derived from
`GIT_EXEC_PATH`. And as `GIT_EXEC_PATH` points to our build directory,
which won't ever contain any of the merge tools, we will fail to locate
any of the merge tools.

This issue has went unnoticed for a long time given that we only skip
bin-wrappers on Windows, and because the CI jobs on Windows didn't
execute due to a bug.

Fix the issue by always setting the `MERGE_TOOL_DIR` environment
variable to the correct directory.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

0 files changed, 0 insertions, 0 deletions