[UNIKRAFT PATCH 6/7] build: `*.in` files as pure pre-processed files

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Registers `*.in` files as purely pre-processed files. The idea is
that such generated files can be used/included by other source
files during pre-processing or compiling.

Example:
 LIBMYLIB_SRCS += $(LIBMYLIB_BASE)/source.m4>.in

Signed-off-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
---
 support/build/Makefile.rules | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/support/build/Makefile.rules b/support/build/Makefile.rules
index 1797d134..1aca3391 100644
--- a/support/build/Makefile.rules
+++ b/support/build/Makefile.rules
@@ -593,6 +593,15 @@ $(eval $(call vprefix_lib,$(1),DTB-y) += $(4))
 $(eval $(call vprefix_lib,$(1),CLEAN-y) += $(call build_clean,$(4)))
 endef
 
+# terminating build rule
+# Only make sure that the file is registered to the preprocess stage
+define buildrule_noop_ =
+UK_PREPROCESS-y += $(2)
+endef
+
+# Aliases for pre-processed files (e.g., *.in)
+buildrule_in   = $(call buildrule_noop_,$(1),$(2))
+
 # wrapper for buildrule_*,
 # selects appropriate buildrule depending on file extension,
 # if there is no such buildrule available, we throw an error.
-- 
2.20.1