Makefile.inc: fix multiple jobs build issue

Certain C source files for coreboot stages require fmap_config.h to
be present. When building coreboot using multiple jobs the dependency
is not always satisfied due to race condition and results in make
error. Work around it by adding fmap_config.h to stage C deps.

Signed-off-by: Michał Żygowski <michal.zygowski@3mdeb.com>
Change-Id: I3a70beedf2eb1c018c5ff98163904253f9a87a61
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69819
Reviewed-by: Nico Huber <nico.h@gmx.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Krystian Hebel <krystian.hebel@3mdeb.com>
diff --git a/Makefile.inc b/Makefile.inc
index 9365a4a..ba4f6fa 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -653,6 +653,14 @@
 postcar-c-deps+=$(DEVICETREE_STATIC_C)
 smm-c-deps+=$(DEVICETREE_STATIC_C)
 
+# Ensure fmap_config.h are created before any objects are compiled
+ramstage-c-deps+=$(obj)/fmap_config.h
+romstage-c-deps+=$(obj)/fmap_config.h
+verstage-c-deps+=$(obj)/fmap_config.h
+bootblock-c-deps+=$(obj)/fmap_config.h
+postcar-c-deps+=$(obj)/fmap_config.h
+smm-c-deps+=$(obj)/fmap_config.h
+
 .PHONY: devicetree
 devicetree: $(DEVICETREE_STATIC_C)