tools/nolibc: add libc-test binary

This can be used to easily compare the behavior of nolibc to the system
libc.
Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

tools/testing/selftests/nolibc/.gitignore

 /initramfs/
+/libc-test
 /nolibc-test
 /run.out
 /sysroot/

tools/testing/selftests/nolibc/Makefile

@@ -94,6 +94,7 @@ help:
 	@echo "  help         this help"
 	@echo "  sysroot      create the nolibc sysroot here (uses \$$ARCH)"
 	@echo "  nolibc-test  build the executable (uses \$$CC and \$$CROSS_COMPILE)"
+	@echo "  libc-test    build an executable using the compiler's default libc instead"
 	@echo "  run-user     runs the executable under QEMU (uses \$$ARCH, \$$TEST)"
 	@echo "  initramfs    prepare the initramfs with nolibc-test"
 	@echo "  defconfig    create a fresh new default config (uses \$$ARCH)"
@@ -128,6 +129,9 @@ nolibc-test: nolibc-test.c sysroot/$(ARCH)/include
 	$(QUIET_CC)$(CC) $(CFLAGS) $(LDFLAGS) -o $@ \
 	  -nostdlib -static -Isysroot/$(ARCH)/include $< -lgcc
 
+libc-test: nolibc-test.c
+	$(QUIET_CC)$(CC) -o $@ $<
+
 # qemu user-land test
 run-user: nolibc-test
 	$(Q)qemu-$(QEMU_ARCH) ./nolibc-test > "$(CURDIR)/run.out" || :
@@ -159,6 +163,8 @@ clean:
 	$(Q)rm -rf sysroot
 	$(call QUIET_CLEAN, nolibc-test)
 	$(Q)rm -f nolibc-test
+	$(call QUIET_CLEAN, libc-test)
+	$(Q)rm -f libc-test
 	$(call QUIET_CLEAN, initramfs)
 	$(Q)rm -rf initramfs
 	$(call QUIET_CLEAN, run.out)