--exec-path not always honored

I noticed this failure if I run git from the build directory:

$ ./git --exec-path=. gc
usage: git pack-objects [{ -q | --progress | --all-progress }]
        [--max-pack-size=N] [--local] [--incremental]
        [--window=N] [--window-memory=N] [--depth=N]
        [--no-reuse-delta] [--no-reuse-object] [--delta-base-offset]
        [--threads=N] [--non-empty] [--revs [--unpacked | --all]*] [--reflog]
        [--include-tag] [--keep-unreachable | --unpack-unreachable]
        --stdout | base-name < ref-or-object-list
error: failed to run repack

The reason is that the version of pack-objects that I have installed in $prefix does not know the option --kept-pack-only, which ./git-repack passes along. It doesn't matter whether I have $prefix in PATH or not.

But on the other hand:

$ ./git --exec-path=. repack -a -d Counting objects: 104070, done. Delta compression using 2 threads. Compressing objects: 100% (26161/26161), done. Writing objects: 100% (104070/104070), done. Total 104070 (delta 76376), reused 104070 (delta 76376)

works just fine whereas without --exec-path it fails like git-gc above.

git-gc is a builtin. Should git setenv("GIT_EXEC_PATH") before it runs other git commands?

-- Hannes