Makefile: fix the "built from commit" code

In ed32b78 (version --build-options: report commit, too, if
possible, 2017-12-15), we introduced code to let `git version
--build-options` report the current commit from which the binaries were
built, if any.

To prevent erroneous commits from being reported (e.g. when unpacking
Git's source code from a .tar.gz file into a subdirectory of a different
Git project, as e.g. git_osx_installer does), we painstakingly set
GIT_CEILING_DIRECTORIES when trying to determine the current commit.

Except that we got the quoting wrong, and that variable therefore does
not have the desired effect.

Let's fix that quoting, and while at it, also suppress the unhelpful
message

fatal: not a git repository (or any of the parent directories): .git

that gets printed to stderr if no current commit could be determined,
and might scare the occasional developer who simply tries to build Git
from scratch.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

Makefile

@@ -2021,8 +2021,9 @@ version.sp version.s version.o: GIT-VERSION-FILE GIT-USER-AGENT
 version.sp version.s version.o: EXTRA_CPPFLAGS = \
 	'-DGIT_VERSION="$(GIT_VERSION)"' \
 	'-DGIT_USER_AGENT=$(GIT_USER_AGENT_CQ_SQ)' \
-	'-DGIT_BUILT_FROM_COMMIT="$(shell GIT_CEILING_DIRECTORIES=\"$(CURDIR)/..\" \
-		git rev-parse -q --verify HEAD || :)"'
+	'-DGIT_BUILT_FROM_COMMIT="$(shell \
+		GIT_CEILING_DIRECTORIES="$(CURDIR)/.." \
+		git rev-parse -q --verify HEAD 2>/dev/null)"'
 
 $(BUILT_INS): git$X
 	$(QUIET_BUILT_IN)$(RM) $@ && \