Makefile: make mandir, htmldir and infodir absolute

This matches the use of the variables with the same names in autotools,
reducing the potential for user surprise.

Using relative paths in these variables also causes issues if they are
exported from the Makefile, as discussed in commit c09d62f (Makefile: do
not export mandir/htmldir/infodir, 2013-02-12).

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -354,33 +354,39 @@ STRIP ?= strip
 # Among the variables below, these:
 #   gitexecdir
 #   template_dir
-#   mandir
-#   infodir
-#   htmldir
 #   sysconfdir
 # can be specified as a relative path some/where/else;
 # this is interpreted as relative to $(prefix) and "git" at
 # runtime figures out where they are based on the path to the executable.
+# Additionally, the following will be treated as relative by "git" if they
+# begin with "$(prefix)/":
+#   mandir
+#   infodir
+#   htmldir
 # This can help installing the suite in a relocatable way.
 
 prefix = $(HOME)
 bindir_relative = bin
 bindir = $(prefix)/$(bindir_relative)
-mandir = share/man
-infodir = share/info
+mandir = $(prefix)/share/man
+infodir = $(prefix)/share/info
 gitexecdir = libexec/git-core
 mergetoolsdir = $(gitexecdir)/mergetools
 sharedir = $(prefix)/share
 gitwebdir = $(sharedir)/gitweb
 localedir = $(sharedir)/locale
 template_dir = share/git-core/templates
-htmldir = share/doc/git-doc
+htmldir = $(prefix)/share/doc/git-doc
 ETC_GITCONFIG = $(sysconfdir)/gitconfig
 ETC_GITATTRIBUTES = $(sysconfdir)/gitattributes
 lib = lib
 # DESTDIR =
 pathsep = :
 
+mandir_relative = $(patsubst $(prefix)/%,%,$(mandir))
+infodir_relative = $(patsubst $(prefix)/%,%,$(infodir))
+htmldir_relative = $(patsubst $(prefix)/%,%,$(htmldir))
+
 export prefix bindir sharedir sysconfdir gitwebdir localedir
 
 CC = cc
@@ -1999,12 +2005,12 @@ ETC_GITATTRIBUTES_SQ = $(subst ','\'',$(ETC_GITATTRIBUTES))
 DESTDIR_SQ = $(subst ','\'',$(DESTDIR))
 bindir_SQ = $(subst ','\'',$(bindir))
 bindir_relative_SQ = $(subst ','\'',$(bindir_relative))
-mandir_SQ = $(subst ','\'',$(mandir))
-infodir_SQ = $(subst ','\'',$(infodir))
+mandir_relative_SQ = $(subst ','\'',$(mandir_relative))
+infodir_relative_SQ = $(subst ','\'',$(infodir_relative))
 localedir_SQ = $(subst ','\'',$(localedir))
 gitexecdir_SQ = $(subst ','\'',$(gitexecdir))
 template_dir_SQ = $(subst ','\'',$(template_dir))
-htmldir_SQ = $(subst ','\'',$(htmldir))
+htmldir_relative_SQ = $(subst ','\'',$(htmldir_relative))
 prefix_SQ = $(subst ','\'',$(prefix))
 gitwebdir_SQ = $(subst ','\'',$(gitwebdir))
 
@@ -2136,9 +2142,9 @@ strip: $(PROGRAMS) git$X
 
 git.sp git.s git.o: GIT-PREFIX
 git.sp git.s git.o: EXTRA_CPPFLAGS = \
-	'-DGIT_HTML_PATH="$(htmldir_SQ)"' \
-	'-DGIT_MAN_PATH="$(mandir_SQ)"' \
-	'-DGIT_INFO_PATH="$(infodir_SQ)"'
+	'-DGIT_HTML_PATH="$(htmldir_relative_SQ)"' \
+	'-DGIT_MAN_PATH="$(mandir_relative_SQ)"' \
+	'-DGIT_INFO_PATH="$(infodir_relative_SQ)"'
 
 git$X: git.o GIT-LDFLAGS $(BUILTIN_OBJS) $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ git.o \
@@ -2148,9 +2154,9 @@ help.sp help.s help.o: common-cmds.h
 
 builtin/help.sp builtin/help.s builtin/help.o: common-cmds.h GIT-PREFIX
 builtin/help.sp builtin/help.s builtin/help.o: EXTRA_CPPFLAGS = \
-	'-DGIT_HTML_PATH="$(htmldir_SQ)"' \
-	'-DGIT_MAN_PATH="$(mandir_SQ)"' \
-	'-DGIT_INFO_PATH="$(infodir_SQ)"'
+	'-DGIT_HTML_PATH="$(htmldir_relative_SQ)"' \
+	'-DGIT_MAN_PATH="$(mandir_relative_SQ)"' \
+	'-DGIT_INFO_PATH="$(infodir_relative_SQ)"'
 
 version.sp version.s version.o: GIT-VERSION-FILE GIT-USER-AGENT
 version.sp version.s version.o: EXTRA_CPPFLAGS = \