rampayload: Add the linuxcheck payload

The i386.c file uses standard 3f8 UART for some simple diagnostic
prints, and the libpayload console otherwise.

This payload was used to debug Linux as a rampayload and was very helpful
for that work.

Change-Id: I1cce5528780cd825fd91a88137fa70abd9f218e7
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: https://review.coreboot.org/28600
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/linuxcheck/Makefile

@@ -0,0 +1,37 @@
+LIBPAYLOAD_DIR=$(CURDIR)/libpayload
+XCOMPILE=$(LIBPAYLOAD_DIR)/libpayload.xcompile
+# build libpayload and put .config file in $(CURDIR) instead of ../libpayload
+# to avoid pollute the libpayload source directory and possible conflicts
+LPOPTS=obj="$(CURDIR)/build" DESTDIR="$(CURDIR)" DOTCONFIG="$(CURDIR)/.config"
+CFLAGS += -Wall -Werror -Os -ffreestanding -nostdinc -nostdlib
+ifeq ($(CONFIG_ARCH_X86),y)
+TARGETARCH = i386
+endif
+
+all: linuxcheck.elf
+
+$(LIBPAYLOAD_DIR):
+	$(MAKE) -C ../libpayload $(LPOPTS) defconfig
+	$(MAKE) -C ../libpayload $(LPOPTS)
+	$(MAKE) -C ../libpayload $(LPOPTS) install
+
+ifneq ($(strip $(wildcard libpayload)),)
+include $(XCOMPILE)
+LPGCC = CC="$(GCC_CC_x86_32)" "$(LIBPAYLOAD_DIR)/bin/lpgcc"
+%.elf: %.c Makefile
+	$(LPGCC) $(CFLAGS) -o $*.elf $*.c $(TARGETARCH).c
+else
+# If libpayload is not found, first build libpayload,
+# then do the make, this time it'll find libpayload
+# and generate the linuxcheck.elf target
+%.elf: $(LIBPAYLOAD_DIR)
+	$(MAKE) all
+endif
+
+clean:
+	rm -f linuxcheck.elf
+
+distclean: clean
+	rm -rf build libpayload .config .config.old
+
+.PHONY: all clean distclean