libgo patch committed: Only rebuild package if dependent .gox changed

[Ian Lance Taylor <iant at golang dot org>]

This patch to libgo tweaks the libgo Makefile so that we only rebuild
a package if the .gox file of some imported package changes.  We now
use mvifdiff and stamp files to track whether a .gox file has changed.
When package A depends on package B, and we rebuild package B, we only
rebuild package A if package B's .gox file changes.  This is safe
because when package A imports package B it only reads package B's
.gox file.  This means that changes that do not affect export
information will not cause dependent packages to be recompiled.  This
doesn't matter in a clean build, but it speeds up an incremental build
when the export information does not change.  Bootstrapped and ran Go
testsuite on x86_64-pc-linux-gnu.  Committed to mainline.

Ian

Attachment: patch.txt
Description: Text document