[PATCH v2] build: do not automatically reconfigure unless configure.ac changed

[Jonathan Nieder <jrnieder@gmail.com>]

Starting with v1.7.12-rc0~4^2 (build: reconfigure automatically if
configure.ac changes, 2012-07-19), configure is automatically run
every time the "configure" script changes.  In particular, that
means configure is automatically rerun whenever the version number
changes (which changes the configure script to support "./configure
--helpe"), which makes bisecting painfully slow.

The intent was to make the reconfiguration process only trigger for
changes to configure.ac's logic.  Tweak the Makefile rule to match
that intent by depending on configure.ac instead of configure.

Reported-by: Martin von Zweigbergk <martinvonz@gmail.com>
Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
---
Martin von Zweigbergk wrote:

> The next line just outside the context here does depend on
> 'configure', which is why I thought this would not be right.

Yes, the 'configure' script that is run needs to reflect the changes
to configure.ac.  Hopefully this version will work better.

 Makefile | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 736ecd45..be3bbcd4 100644
--- a/Makefile
+++ b/Makefile
@@ -2275,10 +2275,11 @@ configure: configure.ac GIT-VERSION-FILE
 	$(RM) $<+
 
 ifdef AUTOCONFIGURED
-config.status: configure
+config.status: configure.ac
 	$(QUIET_GEN)if test -f config.status; then \
 	  ./config.status --recheck; \
 	else \
+	  $(MAKE) configure && \
 	  ./configure; \
 	fi
 reconfigure config.mak.autogen: config.status
-- 
1.8.1