Merge branch 'ab/make-cleanup'

Reorganize Makefile to allow building git.o and other essential
objects without extra stuff needed only for testing.

* ab/make-cleanup:
  Makefile: add {program,xdiff,test,git,fuzz}-objs & objects targets
  Makefile: split OBJECTS into OBJECTS and GIT_OBJS
  Makefile: sort OBJECTS assignment for subsequent change
  Makefile: split up long OBJECTS line
  Makefile: guard against TEST_OBJS in the environment

Makefile

@@ -578,7 +578,9 @@ GENERATED_H =
 EXTRA_CPPFLAGS =
 FUZZ_OBJS =
 FUZZ_PROGRAMS =
+GIT_OBJS =
 LIB_OBJS =
+OBJECTS =
 PROGRAM_OBJS =
 PROGRAMS =
 EXCLUDED_PROGRAMS =
@@ -587,6 +589,7 @@ SCRIPT_PYTHON =
 SCRIPT_SH =
 SCRIPT_LIB =
 TEST_BUILTINS_OBJS =
+TEST_OBJS =
 TEST_PROGRAMS_NEED_X =
 THIRD_PARTY_SOURCES =
 
@@ -662,6 +665,8 @@ ETAGS_TARGET = TAGS
 FUZZ_OBJS += fuzz-commit-graph.o
 FUZZ_OBJS += fuzz-pack-headers.o
 FUZZ_OBJS += fuzz-pack-idx.o
+.PHONY: fuzz-objs
+fuzz-objs: $(FUZZ_OBJS)
 
 # Always build fuzz objects even if not testing, to prevent bit-rot.
 all:: $(FUZZ_OBJS)
@@ -679,6 +684,8 @@ PROGRAM_OBJS += http-backend.o
 PROGRAM_OBJS += imap-send.o
 PROGRAM_OBJS += sh-i18n--envsubst.o
 PROGRAM_OBJS += shell.o
+.PHONY: program-objs
+program-objs: $(PROGRAM_OBJS)
 
 # Binary suffix, set to .exe for Windows builds
 X =
@@ -2378,16 +2385,30 @@ XDIFF_OBJS += xdiff/xmerge.o
 XDIFF_OBJS += xdiff/xpatience.o
 XDIFF_OBJS += xdiff/xprepare.o
 XDIFF_OBJS += xdiff/xutils.o
+.PHONY: xdiff-objs
+xdiff-objs: $(XDIFF_OBJS)
 
 TEST_OBJS := $(patsubst %$X,%.o,$(TEST_PROGRAMS)) $(patsubst %,t/helper/%,$(TEST_BUILTINS_OBJS))
-OBJECTS := $(LIB_OBJS) $(BUILTIN_OBJS) $(PROGRAM_OBJS) $(TEST_OBJS) \
-	$(XDIFF_OBJS) \
-	$(FUZZ_OBJS) \
-	common-main.o \
-	git.o
+.PHONY: test-objs
+test-objs: $(TEST_OBJS)
+
+GIT_OBJS += $(LIB_OBJS)
+GIT_OBJS += $(BUILTIN_OBJS)
+GIT_OBJS += common-main.o
+GIT_OBJS += git.o
+.PHONY: git-objs
+git-objs: $(GIT_OBJS)
+
+OBJECTS += $(GIT_OBJS)
+OBJECTS += $(PROGRAM_OBJS)
+OBJECTS += $(TEST_OBJS)
+OBJECTS += $(XDIFF_OBJS)
+OBJECTS += $(FUZZ_OBJS)
 ifndef NO_CURL
 	OBJECTS += http.o http-walker.o remote-curl.o
 endif
+.PHONY: objects
+objects: $(OBJECTS)
 
 dep_files := $(foreach f,$(OBJECTS),$(dir $f).depend/$(notdir $f).d)
 dep_dirs := $(addsuffix .depend,$(sort $(dir $(OBJECTS))))