help: add shell-path to --build-options

It may be useful to know which shell Git was built to try to point to,
in the event that shell-based Git commands are failing. $SHELL_PATH is
set during the build and used to launch the manpage viewer, as well as
by git-compat-util.h, and it's used during tests. 'git version
--build-options' is encouraged for use in bug reports, so it makes sense
to include this information there.

Signed-off-by: Emily Shaffer <emilyshaffer@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

help.c

@@ -641,6 +641,7 @@ void get_version_info(struct strbuf *buf, int show_build_options)
 			strbuf_addstr(buf, "no commit associated with this build\n");
 		strbuf_addf(buf, "sizeof-long: %d\n", (int)sizeof(long));
 		strbuf_addf(buf, "sizeof-size_t: %d\n", (int)sizeof(size_t));
+		strbuf_addf(buf, "shell-path: %s\n", SHELL_PATH);
 		/* NEEDSWORK: also save and output GIT-BUILD_OPTIONS? */
 	}
 }