t/helper: add an empty test-tool program

This will become an umbrella program that absorbs most [1] t/helper
programs in. By having a single executable binary we reduce disk usage
(libgit.a is replicated by every t/helper program) and shorten link
time a bit.

Running "make --jobs=1; du -sh t/helper" with ccache fully populated,
it takes 27 seconds and 277MB at the beginning of this series, 17
seconds and 42MB at the end.

[1] There are a couple programs that will not become part of
    test-tool: test-line-buffer and test-svn-fe have extra
    dependencies and test-fake-ssh's program name has to be a single
    word for some ssh tests.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -546,6 +546,7 @@ SCRIPT_PERL =
 SCRIPT_PYTHON =
 SCRIPT_SH =
 SCRIPT_LIB =
+TEST_BUILTINS_OBJS =
 TEST_PROGRAMS_NEED_X =
 
 # Having this variable in your environment would break pipelines because
@@ -690,6 +691,7 @@ TEST_PROGRAMS_NEED_X += test-string-list
 TEST_PROGRAMS_NEED_X += test-submodule-config
 TEST_PROGRAMS_NEED_X += test-subprocess
 TEST_PROGRAMS_NEED_X += test-svn-fe
+TEST_PROGRAMS_NEED_X += test-tool
 TEST_PROGRAMS_NEED_X += test-urlmatch-normalization
 TEST_PROGRAMS_NEED_X += test-wildmatch
 
@@ -2083,7 +2085,7 @@ VCSSVN_OBJS += vcs-svn/fast_export.o
 VCSSVN_OBJS += vcs-svn/svndiff.o
 VCSSVN_OBJS += vcs-svn/svndump.o
 
-TEST_OBJS := $(patsubst %$X,%.o,$(TEST_PROGRAMS))
+TEST_OBJS := $(patsubst %$X,%.o,$(TEST_PROGRAMS)) $(patsubst %,t/helper/%,$(TEST_BUILTINS_OBJS))
 OBJECTS := $(LIB_OBJS) $(BUILTIN_OBJS) $(PROGRAM_OBJS) $(TEST_OBJS) \
 	$(XDIFF_OBJS) \
 	$(VCSSVN_OBJS) \
@@ -2494,6 +2496,8 @@ t/helper/test-svn-fe$X: $(VCSSVN_LIB)
 
 .PRECIOUS: $(TEST_OBJS)
 
+t/helper/test-tool$X: $(patsubst %,t/helper/%,$(TEST_BUILTINS_OBJS))
+
 t/helper/test-%$X: t/helper/test-%.o GIT-LDFLAGS $(GITLIBS)
 	$(QUIET_LINK)$(CC) $(ALL_CFLAGS) -o $@ $(ALL_LDFLAGS) $(filter %.o,$^) $(filter %.a,$^) $(LIBS)
 

t/helper/test-tool.c

@@ -0,0 +1,27 @@
+#include "git-compat-util.h"
+#include "test-tool.h"
+
+struct test_cmd {
+	const char *name;
+	int (*fn)(int argc, const char **argv);
+};
+
+static struct test_cmd cmds[] = {
+};
+
+int cmd_main(int argc, const char **argv)
+{
+	int i;
+
+	if (argc < 2)
+		die("I need a test name!");
+
+	for (i = 0; i < ARRAY_SIZE(cmds); i++) {
+		if (!strcmp(cmds[i].name, argv[1])) {
+			argv++;
+			argc--;
+			return cmds[i].fn(argc, argv);
+		}
+	}
+	die("There is no test named '%s'", argv[1]);
+}

t/helper/test-tool.h

@@ -0,0 +1,4 @@
+#ifndef __TEST_TOOL_H__
+#define __TEST_TOOL_H__
+
+#endif