Re: [PATCH 3/3] pager: properly log pager exit code when signalled

When git invokes a pager that exits with non-zero the common case is
that we'll already return the correct SIGPIPE failure from git itself,
but the exit code logged in trace2 has always been incorrectly
reported[1]. Fix that and log the correct exit code in the logs.

Since this gives us something to test outside of our recently-added
tests needing a !MINGW prerequisite, let's refactor the test to run on
MINGW and actually check for SIGPIPE outside of MINGW.

The wait_or_whine() is only called with a true "in_signal" from from
finish_command_in_signal(), which in turn is only used in pager.c.

I'm not quite sure about that BUG() case. Can we have a true in_signal
and not have a true WIFEXITED(status)? I haven't been able to think of
a test case for it.

1. The incorrect logging of the exit code in was seemingly copy/pasted
   into finish_command_in_signal() in ee4512ed481 (trace2: create new
   combined trace facility, 2019-02-22)

Signed-off-by: Ævar Arnfjörð Bjarmason <redacted>
---
 run-command.c    |  8 +++++--
 t/t7006-pager.sh | 61 +++++++++++++++++++++++++++++++++++++++++-------
 2 files changed, 58 insertions(+), 11 deletions(-)

diff --git a/run-command.c b/run-command.c
index ea4d0fb4b15..10e1c96c2bd 100644
--- a/run-command.c
+++ b/run-command.c

@@ -551,8 +551,12 @@ static int wait_or_whine(pid_t pid, const char *argv0, int in_signal)
 
 	while ((waiting = waitpid(pid, &status, 0)) < 0 && errno == EINTR)
 		;	/* nothing */
-	if (in_signal)
-		return 0;
+	if (in_signal && WIFEXITED(status))
+		return WEXITSTATUS(status);
+	if (in_signal) {
+		BUG("was not expecting waitpid() status %d", status);
+		return -1;
+	}