Makefile: NO_INSTALL_HARDLINKS

Your filesystem may support hardlinks, but you may choose not to use them
when installing git-foo builtins and favor symblic links or copies for
whatever reason.

The installation procedure of git-gui/ directory is not touched with this
patch and git-citool still ends up being a hardlink to git-gui, but it
needs to be addressed separately.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -244,6 +244,9 @@ all::
 # Define NO_CROSS_DIRECTORY_HARDLINKS if you plan to distribute the installed
 # programs as a tar, where bin/ and libexec/ might be on different file systems.
 #
+# Define NO_INSTALL_HARDLINKS if you prefer to use either symbolic links or
+# copies to install built-in git commands e.g. git-cat-file.
+#
 # Define USE_NED_ALLOCATOR if you want to replace the platforms default
 # memory allocators with the nedmalloc allocator written by Niall Douglas.
 #
@@ -1777,6 +1780,10 @@ ifdef ASCIIDOC7
 	export ASCIIDOC7
 endif
 
+ifdef NO_INSTALL_HARDLINKS
+	export NO_INSTALL_HARDLINKS
+endif
+
 ### profile feedback build
 #
 
@@ -2482,26 +2489,29 @@ endif
 	{ test "$$bindir/" = "$$execdir/" || \
 	  for p in git$X $(filter $(install_bindir_programs),$(ALL_PROGRAMS)); do \
 		$(RM) "$$execdir/$$p" && \
-		test -z "$(NO_CROSS_DIRECTORY_HARDLINKS)" && \
+		test -z "$(NO_INSTALL_HARDLINKS)$(NO_CROSS_DIRECTORY_HARDLINKS)" && \
 		ln "$$bindir/$$p" "$$execdir/$$p" 2>/dev/null || \
 		cp "$$bindir/$$p" "$$execdir/$$p" || exit; \
 	  done; \
 	} && \
 	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; \
 	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; \
 	done && \
 	remote_curl_aliases="$(REMOTE_CURL_ALIASES)" && \
 	for p in $$remote_curl_aliases; do \
 		$(RM) "$$execdir/$$p" && \
+		test -z "$(NO_INSTALL_HARDLINKS)" && \
 		ln "$$execdir/git-remote-http$X" "$$execdir/$$p" 2>/dev/null || \
 		ln -s "git-remote-http$X" "$$execdir/$$p" 2>/dev/null || \
 		cp "$$execdir/git-remote-http$X" "$$execdir/$$p" || exit; \