[PATCH v5 1/4] rust: export BINDGEN_TARGET from a separate Makefile

[Asuna Yang <spriteovo@gmail.com>]

From: Asuna Yang <spriteovo@gmail.com>

A subsequent commit will add a new function `bindgen-option` to
`scripts/Kconfig.include`. The bindgen backend requires the `--target`
option for cross compiling, but variable `BINDGEN_TARGET` in
`rust/Makefile` cannot be exported to `scripts/Kconfig.include`.

Therefore, move this variable to a separate new `Makefile.rust` file and
include it from `scripts/Makefile` to make the exported variable
available for use in Kconfig. Place the include in the `need-compiler`
branch to avoid including it in irrelevant make targets.

Since the new file name is `Makefile.rust`, it matches an existing
MAINTAINERS rule `scripts/*rust*`, so no modification to the MAINTAINERS
file is needed.

Signed-off-by: Asuna Yang <SpriteOvO@gmail.com>
---
 Makefile              | 3 ++-
 rust/Makefile         | 8 --------
 scripts/Makefile.rust | 9 +++++++++
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/Makefile b/Makefile
index e61f1300fea0..bdbf2025e68c 100644
--- a/Makefile
+++ b/Makefile
@@ -718,9 +718,10 @@ ifneq ($(findstring clang,$(CC_VERSION_TEXT)),)
 include $(srctree)/scripts/Makefile.clang
 endif
 
+ifdef need-compiler
+include $(srctree)/scripts/Makefile.rust
 # Include this also for config targets because some architectures need
 # cc-cross-prefix to determine CROSS_COMPILE.
-ifdef need-compiler
 include $(srctree)/scripts/Makefile.compiler
 endif
 
diff --git a/rust/Makefile b/rust/Makefile
index 5d357dce1704..2603b34f9833 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -385,14 +385,6 @@ bindgen_skip_c_flags := -mno-fp-ret-in-387 -mpreferred-stack-boundary=% \
 	-fzero-init-padding-bits=% -mno-fdpic \
 	--param=% --param asan-% -fno-isolate-erroneous-paths-dereference
 
-# Derived from `scripts/Makefile.clang`.
-BINDGEN_TARGET_x86	:= x86_64-linux-gnu
-BINDGEN_TARGET_arm64	:= aarch64-linux-gnu
-BINDGEN_TARGET_arm	:= arm-linux-gnueabi
-BINDGEN_TARGET_loongarch	:= loongarch64-linux-gnusf
-BINDGEN_TARGET_um	:= $(BINDGEN_TARGET_$(SUBARCH))
-BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))
-
 # All warnings are inhibited since GCC builds are very experimental,
 # many GCC warnings are not supported by Clang, they may only appear in
 # some configurations, with new GCC versions, etc.
diff --git a/scripts/Makefile.rust b/scripts/Makefile.rust
new file mode 100644
index 000000000000..5c12b4b8c8b6
--- /dev/null
+++ b/scripts/Makefile.rust
@@ -0,0 +1,9 @@
+# Derived from `scripts/Makefile.clang`.
+BINDGEN_TARGET_x86	:= x86_64-linux-gnu
+BINDGEN_TARGET_arm64	:= aarch64-linux-gnu
+BINDGEN_TARGET_arm	:= arm-linux-gnueabi
+BINDGEN_TARGET_loongarch	:= loongarch64-linux-gnusf
+BINDGEN_TARGET_um	:= $(BINDGEN_TARGET_$(SUBARCH))
+BINDGEN_TARGET		:= $(BINDGEN_TARGET_$(SRCARCH))
+
+export BINDGEN_TARGET

-- 
2.51.1