nvramcui: Update Makefile

- Add all, clean and distclean to .PHONY
- Rebuild nvramcui.elf when the makefile changes.
- Update libpayload target to $(LIBPAYLOAD_DIR) target - these are the
same thing, but by using the variable it makes it more obvious.
- Remove .config.old as well as .config when running distclean.
- Add CFLAGS to the LPGCC command line:
-- Enable all warnings, set warnings as errors.
-- Optimize for size
-- Enable '-ffreestanding -nostdinc -nostdlib' to keep from building in
system functions and to fix the warning:
libpayload.h: warning: conflicting types for built-in function 'log2'
static inline int log2(u32 x) { return sizeof(x) * 8 - clz(x) - 1; }

Change-Id: Icc6c70b259cd7c22dc960cdb732927f9c0c93ee8
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/14482
Tested-by: build bot (Jenkins)
Reviewed-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

payloads/nvramcui/Makefile

@@ -3,10 +3,11 @@ 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
 
 all: nvramcui.elf
 
-libpayload:
+$(LIBPAYLOAD_DIR):
 	$(MAKE) -C ../libpayload $(LPOPTS) defconfig
 	$(MAKE) -C ../libpayload $(LPOPTS)
 	$(MAKE) -C ../libpayload $(LPOPTS) install
@@ -14,19 +15,20 @@ libpayload:
 ifneq ($(strip $(wildcard libpayload)),)
 include $(XCOMPILE)
 LPGCC = CC="$(GCC_CC_x86_32)" "$(LIBPAYLOAD_DIR)/bin/lpgcc"
-%.elf: %.c
-	$(LPGCC) -o $*.elf $*.c
+%.elf: %.c Makefile
+	$(LPGCC) $(CFLAGS) -o $*.elf $*.c
 else
 # If libpayload is not found, first build libpayload,
 # then do the make, this time it'll find libpayload
 # and generate the nvramcui.elf target
-%.elf: libpayload
+%.elf: $(LIBPAYLOAD_DIR)
 	$(MAKE) all
 endif
 
-.PHONY:
 clean:
 	rm -f nvramcui.elf
 
 distclean: clean
-	rm -rf build libpayload .config
+	rm -rf build libpayload .config .config.old
+
+.PHONY: all clean distclean