[UNIKRAFT PATCH 3/7] build: Per-file flags and includes for M4 pre-processing

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Similar to build rules, we add support for specifying file-local
flags and includes to M4 pre-processing rules. This can be done
through the following variables:
 <LIBNAME>_<SOURCE NAME>_M4FLAGS
 <LIBNAME>_<SOURCE NAME>_M4INCLUDES

Example: Setting `-myflag` to the M4 pre-processing of `code.m4`:
 LIBMYLIB_SRCS += $(LIBMYLIB_BASE)/code.m4>.c
 LIBMYLIB_CODE_M4FLAGS += -myflag

Signed-off-by: Simon Kuenzer <simon.kuenzer@xxxxxxxxx>
---
 support/build/Makefile.rules | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/support/build/Makefile.rules b/support/build/Makefile.rules
index 44701cd2..6a8c2099 100644
--- a/support/build/Makefile.rules
+++ b/support/build/Makefile.rules
@@ -622,8 +622,10 @@ $(3): $(2) | prepare
        $(call build_cmd,M4,$(1),$(3),\
                $(M4)  $$(M4INCLUDES) $$(M4INCLUDES-y) \
                       $$($(call vprefix_lib,$(1),M4INCLUDES)) $$($(call 
vprefix_lib,$(1),M4INCLUDES-y)) \
+                      $$($(call vprefix_src,$(1),$(2),,M4INCLUDES)) $$($(call 
vprefix_src,$(1),$(2),,M4INCLUDES-y)) \
                       $$(M4FLAGS) $$(M4FLAGS-y) \
                       $$($(call vprefix_lib,$(1),M4FLAGS)) $$($(call 
vprefix_lib,$(1),M4FLAGS-y)) \
+                      $$($(call vprefix_src,$(1),$(2),,M4FLAGS)) $$($(call 
vprefix_src,$(1),$(2),,M4FLAGS-y)) \
                       $(4) \
                       $(2) > $(3)
        )
-- 
2.20.1