[PATCH v2] Makefile: Pass relative paths to the compiler.

[Vagrant Cascadian]

Upstream commit 12753d22563f7d2d01f2c6644c7b66b06eb5c90f introduced
uses of __FILE__ which may result in the build path getting embedded
into the resulting binary.

https://reproducible-builds.org/docs/build-path/

Signed-off-by: Vagrant Cascadian <vagrant at reproducible-builds.org>
Cc: Xiang W <wxjstz at 126.com>
Cc: Anup Patel <anup at brainfault.org>
---
Changes since v1:

* Pass relative paths to the compiler instead of using
  -ffile-prefix-map to strip out the full paths, as suggested by Xiang
  W.

 Makefile | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index 8623c1c..d017534 100644
--- a/Makefile
+++ b/Makefile
@@ -361,7 +361,7 @@ compile_cc_dep = $(CMD_PREFIX)mkdir -p `dirname $(1)`; \
 	       -MM $(2) >> $(1) || rm -f $(1)
 compile_cc = $(CMD_PREFIX)mkdir -p `dirname $(1)`; \
 	     echo " CC        $(subst $(build_dir)/,,$(1))"; \
-	     $(CC) $(CFLAGS) $(call dynamic_flags,$(1),$(2)) -c $(2) -o $(1)
+	     $(CC) $(CFLAGS) $(call dynamic_flags,$(1),$(2)) -c $(subst $(src_dir)/,,$(2)) -o $(1)
 compile_as_dep = $(CMD_PREFIX)mkdir -p `dirname $(1)`; \
 	     echo " AS-DEP    $(subst $(build_dir)/,,$(1))"; \
 	     printf %s `dirname $(1)`/ > $(1) && \
-- 
2.30.2