Merge 'git-wrapper' into HEAD

Use msysGit's `git-wrapper` instead of the builtins. This works around
two issues:

- when the file system does not allow hard links, we would waste over
  800 megabyte by having 109 copies of a multi-megabyte executable

- even when the file system allows hard links, the Windows Explorer
  counts the disk usage as if it did not. Many users complained about
  Git for Windows using too much space (when it actually did not). We
  can easily avoid those user complaints by merging this branch.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Makefile

@@ -1678,11 +1678,17 @@ version.sp version.s version.o: EXTRA_CPPFLAGS = \
 	'-DGIT_VERSION="$(GIT_VERSION)"' \
 	'-DGIT_USER_AGENT=$(GIT_USER_AGENT_CQ_SQ)'
 
+ifeq (,$(BUILT_IN_WRAPPER))
 $(BUILT_INS): git$X
 	$(QUIET_BUILT_IN)$(RM) $@ && \
 	ln $< $@ 2>/dev/null || \
 	ln -s $< $@ 2>/dev/null || \
 	cp $< $@
+else
+$(BUILT_INS): $(BUILT_IN_WRAPPER)
+	$(QUIET_BUILT_IN)$(RM) $@ && \
+	cp $< $@
+endif
 
 common-cmds.h: ./generate-cmdlist.sh command-list.txt
 
@@ -2246,6 +2252,24 @@ profile-install: profile
 profile-fast-install: profile-fast
 	$(MAKE) install
 
+ifeq (,$(BUILT_IN_WRAPPER))
+LN_OR_CP_BUILT_IN_BINDIR = \
+	test -z "$(NO_INSTALL_HARDLINKS)" && \
+	ln "$$bindir/git$X" "$$bindir/$$p" 2>/dev/null || \
+	ln -s "git$X" "$$bindir/$$p" 2>/dev/null || \
+	cp "$$bindir/git$X" "$$bindir/$$p" || exit;
+LN_OR_CP_BUILT_IN_EXECDIR = \
+	test -z "$(NO_INSTALL_HARDLINKS)" && \
+	ln "$$execdir/git$X" "$$execdir/$$p" 2>/dev/null || \
+	ln -s "git$X" "$$execdir/$$p" 2>/dev/null || \
+	cp "$$execdir/git$X" "$$execdir/$$p" || exit;
+else
+LN_OR_CP_BUILT_IN_BINDIR = \
+	cp "$(BUILT_IN_WRAPPER)" "$$bindir/$$p" || exit;
+LN_OR_CP_BUILT_IN_EXECDIR = \
+	cp "$(BUILT_IN_WRAPPER)" "$$execdir/$$p" || exit;
+endif
+
 install: all
 	$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(bindir_SQ)'
 	$(INSTALL) -d -m 755 '$(DESTDIR_SQ)$(gitexec_instdir_SQ)'
@@ -2284,17 +2308,11 @@ endif
 	} && \
 	for p in $(filter $(install_bindir_programs),$(BUILT_INS)); do \
 		$(RM) "$$bindir/$$p" && \
-		test -z "$(NO_INSTALL_HARDLINKS)" && \
-		ln "$$bindir/git$X" "$$bindir/$$p" 2>/dev/null || \
-		ln -s "git$X" "$$bindir/$$p" 2>/dev/null || \
-		cp "$$bindir/git$X" "$$bindir/$$p" || exit; \
+		$(LN_OR_CP_BUILT_IN_BINDIR) \
 	done && \
 	for p in $(BUILT_INS); do \
 		$(RM) "$$execdir/$$p" && \
-		test -z "$(NO_INSTALL_HARDLINKS)" && \
-		ln "$$execdir/git$X" "$$execdir/$$p" 2>/dev/null || \
-		ln -s "git$X" "$$execdir/$$p" 2>/dev/null || \
-		cp "$$execdir/git$X" "$$execdir/$$p" || exit; \
+		$(LN_OR_CP_BUILT_IN_EXECDIR) \
 	done && \
 	remote_curl_aliases="$(REMOTE_CURL_ALIASES)" && \
 	for p in $$remote_curl_aliases; do \