Merge branch 'pr/use-default-sigpipe-setting'

We used to get confused when a process called us with SIGPIPE
ignored; we do want to die with SIGPIPE when the output is not
read by default, and do ignore the signal when appropriate.

* pr/use-default-sigpipe-setting:
  mingw.h: add dummy functions for sigset_t operations
  unblock and unignore SIGPIPE

git.c

@@ -592,6 +592,26 @@ static int run_argv(int *argcp, const char ***argv)
 	return done_alias;
 }
 
+/*
+ * Many parts of Git have subprograms communicate via pipe, expect the
+ * upstream of a pipe to die with SIGPIPE when the downstream of a
+ * pipe does not need to read all that is written.  Some third-party
+ * programs that ignore or block SIGPIPE for their own reason forget
+ * to restore SIGPIPE handling to the default before spawning Git and
+ * break this carefully orchestrated machinery.
+ *
+ * Restore the way SIGPIPE is handled to default, which is what we
+ * expect.
+ */
+static void restore_sigpipe_to_default(void)
+{
+	sigset_t unblock;
+
+	sigemptyset(&unblock);
+	sigaddset(&unblock, SIGPIPE);
+	sigprocmask(SIG_UNBLOCK, &unblock, NULL);
+	signal(SIGPIPE, SIG_DFL);
+}
 
 int main(int argc, char **av)
 {
@@ -611,6 +631,8 @@ int main(int argc, char **av)
 	 */
 	sanitize_stdfds();
 
+	restore_sigpipe_to_default();
+
 	git_setup_gettext();
 
 	trace_command_performance(argv);