util/kconfig: Add pre-built parser

It avoids the dependency on bison/flex, minimally speeds up the build
and also works around weird race conditions in some versions of bison
that need more investigation.

The issue this avoids manifests as a build error when creating
parser.tab.c:

    input in flex scanner failed
    make: *** [util/kconfig/Makefile.inc:66: build/util/kconfig/parser.tab.c] Error 2

Since the error happens within bison the alternative would be to make
bison part of our crossgcc environment to ensure that no broken OS
build is used.

BUG=b:197515860
TEST=things build with bison not installed

Change-Id: Ib35dfb7beafc0a09dc333e962b1e3f33df46a854
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57409
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

util/kconfig/Makefile.inc

@@ -60,12 +60,25 @@ endef
 
 $(foreach prog,$(hostprogs),$(eval $(call hostprogs_template,$(prog))))
 
+# This might be a bit of a chicken & egg problem, using a kconfig flag when
+# building kconfig, but if you're messing with the parser you probably know
+# what you're doing: make CONFIG_UTIL_GENPARSER=y
+ifeq ($(CONFIG_UTIL_GENPARSER),y)
 $(objk)/%.tab.c $(objk)/%.tab.h: $(srck)/%.y
 	bison -t -l --defines -b $(objk)/$* $<
 
 $(objk)/%.lex.c: $(srck)/%.l
 	flex -L -o$@ $<
 
+else # !CONFIG_UTIL_GENPARSER
+
+$(objk)/parser.tab.c: | $(objk)/parser.tab.h
+
+$(objk)/%: $(srck)/%_shipped
+	cp $< $@
+
+endif
+
 # Support mingw by shipping our own regex implementation
 _OS=$(shell uname -s |cut -c-7)
 regex-objs=