[PATCH v2 0/4] test fixes around valgrind

Updates the valgrind test framework a bit, and then fixes a few issues valgrind has found.

Essentailly the same as the previously posted version, but those suggested fixes squashed in.

I am sending this out as a final "complain now, or this will go to 'next' soonish" warning. The "What's cooking" report is getting crowded with too many topics marked as "Expecting a reroll", and I'm trying to do easier ones myself to see how much reduction we can make.

Ævar Arnfjörð Bjarmason (4):
  tests: using custom GIT_EXEC_PATH breaks --valgrind tests
  log test: skip a failing mkstemp() test under valgrind
  commit-graph.c: don't assume that stat() succeeds
  object-file: fix a unpack_loose_header() regression in 3b6a8db3b03

 commit-graph.c        |  6 ++++--
 object-file.c         |  8 ++++++--
 t/t0060-path-utils.sh |  4 ++--
 t/t1006-cat-file.sh   | 10 ++++++++--
 t/t1450-fsck.sh       | 13 +++++++++++--
 t/t4202-log.sh        | 11 +++++++----
 t/test-lib.sh         |  1 +
 7 files changed, 39 insertions(+), 14 deletions(-)

1:  4ebaddb01d ! 1:  3b79af1dde tests: make RUNTIME_PREFIX compatible with --valgrind
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    tests: make RUNTIME_PREFIX compatible with --valgrind
    +    tests: using custom GIT_EXEC_PATH breaks --valgrind tests
     
         Fix a regression in b7d11a0f5d2 (tests: exercise the RUNTIME_PREFIX
         feature, 2021-07-24) where tests that want to set up and test a "git"
2:  b25609d6fc = 2:  35a7226706 log test: skip a failing mkstemp() test under valgrind
3:  d56edb6654 ! 3:  84d1793178 commit-graph.c: don't assume that stat() succeeds
    @@ Commit message
     
         This would happen as we stat'd the non-existing
         ".git/objects/info/commit-graph" file. Let's fix mark_commit_graphs()
    -    to check the statu() return value, and while we're at it fix another
    +    to check the stat()'s return value, and while we're at it fix another
         case added in the same commit to do the same.
     
         The caller in expire_commit_graphs() would have been less likely to
4:  995cfb0439 = 4:  391ae0a276 object-file: fix a unpack_loose_header() regression in 3b6a8db3b03