[PATCH v2 4/5] Makefile: add the ".DELETE_ON_ERROR" flag

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Use the GNU make ".DELETE_ON_ERROR" flag. As discussed in preceding
commits we're now less paranoid about "mv" failing, let's bring that
paranoia back in a way that makes more sense, and applies to all rules
in the Makefile.

Now if a command to make X fails X will be removed, the default
behavior of GNU make is to only do so if "make" itself is interrupted
with a signal.

E.g. if we now intentionally break one of the rules with:

    -       mv $@+ $@
    +       mv $@+ $@ && \
    +       false

We'll get output like:

    $ make git
        CC git.o
        LINK git
    make: *** [Makefile:2179: git] Error 1
    make: *** Deleting file 'git'
    $ file git
    git: cannot open `git' (No such file or directory)

Before this change we'd leave the file in place in under this
scenario.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Makefile | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Makefile b/Makefile
index f08635067b3..573bce20357 100644
--- a/Makefile
+++ b/Makefile
@@ -2126,6 +2126,16 @@ shell_compatibility_test: please_set_SHELL_PATH_to_a_more_modern_shell
 strip: $(PROGRAMS) git$X
 	$(STRIP) $(STRIP_OPTS) $^
 
+### Flags affecting all rules
+
+# A GNU make extension since gmake 3.72 (released in late 1994) to
+# remove the target of rules if commands in those rules fail. The
+# default is to only do that if make itself receives a signal. Affects
+# all targets, see:
+#
+#    info make --index-search=.DELETE_ON_ERROR
+.DELETE_ON_ERROR:
+
 ### Target-specific flags and dependencies
 
 # The generic compilation pattern rule and automatically
-- 
2.31.1.461.gd47399f6574