Revert "util/abuild: Have abuild generate the .xcompile if it doesn't exist"

This reverts commit 9ff4029db9.

Pulling the toplevel Makefile into a tiny one has all sorts of side
effects. For instance, the toplevel (random) .config is also included
so the results depend on the board that is selected there. What finally
broke it is a line that is unconditionally printed for AMD Picasso
boards resulting in lots of lines like this:

  skipping LENOVO_W520 because we're missing compilers for		\
  (Adding PSP c7ce61492157d3237f679c4a40a08b79				\
  .../coreboot/3rdparty/amd_blobs/picasso/PSP/PspBootLoader_prod_RV.sbin)

While both issues, the random .config and amd/picasso, could be worked
around easily, it seems hard to predict what other pitfalls are lurking
in the Makefile inclusion. Also, the problem solved by its inclusion
can be fixed by a much simpler `make .xcompile`.

Change-Id: I2ff70f561d717eb30e5f3c06c83e83468e174ec5
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41846
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/abuild/abuild

@@ -466,14 +466,13 @@ function build_config
 	required_arches=$(grep -E "^CONFIG_ARCH_(BOOTBLOCK|R.MSTAGE|VERSTAGE)" "$TARGET/${BUILD_NAME}/config.build" | \
 			sed "s,^CONFIG_ARCH_[^_]*_\([^=]*\)=.*$,\1," |sort -u |tr 'A-Z\n\r' 'a-z  ')
 
-	missing_arches="$($MAKE --no-print-directory -f Makefile -f - \
-		REQUIRED_ARCHES="$required_arches" obj="${build_dir}" <<'EOF'
+	missing_arches="$($MAKE --no-print-directory -f - \
+		REQUIRED_ARCHES="$required_arches" <<'EOF'
 include .xcompile
 .PHONY: missing_arches
 missing_arches:
 	$(if $(XCOMPILE_COMPLETE),,$(error .xcompile is invalid.))
 	@echo $(foreach arch,$(REQUIRED_ARCHES),$(if $(filter $(arch),$(SUBARCH_SUPPORTED)),,$(arch)))
-.DEFAULT_GOAL := missing_arches
 EOF
 )"
 	# shellcheck disable=SC2181