msvc: add a Makefile target to pre-generate the VS solution

The entire idea of generating the VS solution makes only sense if we
generate it via Continuous Integration; otherwise potential users would
still have to download the entire Git for Windows SDK.

So let's just add a target in the Makefile that can be used to generate
said solution; The generated files will then be committed so that they
can be pushed to a branch ready to check out by Visual Studio users.

To make things even more useful, we also generate and commit other files
that are required to run the test suite, such as templates and
bin-wrappers: with this, developers can run the test suite in a regular
Git Bash (that is part of a regular Git for Windows installation) after
building the solution in Visual Studio.

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

config.mak.uname

@@ -458,6 +458,65 @@ endif
 	X = .exe
 
 compat/msvc.o: compat/msvc.c compat/mingw.c GIT-CFLAGS
+
+vcxproj:
+	# Require clean work tree
+	git update-index -q --refresh && \
+	git diff-files --quiet && \
+	git diff-index --cached --quiet HEAD --
+
+	# Make .vcxproj files and add them
+	unset QUIET_GEN QUIET_BUILT_IN; \
+	perl contrib/buildsystems/generate -g Vcxproj
+	git add -f git.sln {*,*/lib,t/helper/*}/{packages.config,*.vcxproj}
+
+	# Add command-list.h
+	$(MAKE) MSVC=1 SKIP_VCPKG=1 prefix=/mingw64 command-list.h
+	git add -f command-list.h
+
+	# Add scripts
+	rm -f perl/perl.mak
+	$(MAKE) MSVC=1 prefix=/mingw64 \
+		$(SCRIPT_LIB) $(SCRIPT_SH_GEN) $(SCRIPT_PERL_GEN)
+	# Strip out the sane tool path, needed only for building
+	sed -i '/^git_broken_path_fix ".*/d' git-sh-setup
+	git add -f $(SCRIPT_LIB) $(SCRIPT_SH_GEN) $(SCRIPT_PERL_GEN)
+
+	# Add Perl module
+	$(MAKE) $(LIB_PERL_GEN)
+	git add -f perl/build
+
+	# Add bin-wrappers, for testing
+	rm -rf bin-wrappers/
+	$(MAKE) MSVC=1 prefix=/mingw64 $(test_bindir_programs)
+	# Ensure that the GIT_EXEC_PATH is a Unix-y one, and that the absolute
+	# path of the repository is not hard-coded (GIT_EXEC_PATH will be set
+	# by test-lib.sh according to the current setup)
+	sed -i -e 's/^\(GIT_EXEC_PATH\)=.*/test -n "$${\1##*:*}" ||\
+			\1="$$(cygpath -u "$$\1")"/' \
+		-e "s|'$$(pwd)|\"\$$GIT_EXEC_PATH\"'|g" bin-wrappers/*
+	# Ensure that test-* helpers find the .dll files copied to top-level
+	sed -i 's|^PATH=.*|&:"$$GIT_EXEC_PATH"|' bin-wrappers/test-*
+	# We do not want to force hard-linking builtins
+	sed -i 's|\(git\)-\([-a-z]*\)\.exe"|\1.exe" \2|g' \
+		bin-wrappers/git-{receive-pack,upload-archive}
+	git add -f $(test_bindir_programs)
+	# remote-ext is a builtin, but invoked as if it were external
+	sed 's|receive-pack|remote-ext|g' \
+		<bin-wrappers/git-receive-pack >bin-wrappers/git-remote-ext
+	git add -f bin-wrappers/git-remote-ext
+
+	# Add templates
+	$(MAKE) -C templates
+	git add -f templates/boilerplates.made templates/blt/
+
+	# Add build options
+	$(MAKE) MSVC=1 prefix=/mingw64 GIT-BUILD-OPTIONS
+	git add -f GIT-BUILD-OPTIONS
+
+	# Commit the whole shebang
+	git commit -m "Generate Visual Studio solution" \
+		-m "Auto-generated by \`$(MAKE)$(MAKEFLAGS) $@\`"
 endif
 ifeq ($(uname_S),Interix)
 	NO_INITGROUPS = YesPlease