rust: kbuild: deduplicate pin-init flags

Extract `pin_init{,_internal}-{cfgs,flags}` to reduce duplication.

[ The new variables will be used later on to easily pass them to
  the `scripts/generate_rust_analyzer.py` script. - Miguel ]

Acked-by: Benno Lossin <lossin@kernel.org>
Signed-off-by: Tamir Duberstein <tamird@kernel.org>
Link: https://patch.msgid.link/20260127-rust-analyzer-pin-init-duplication-v3-1-118c48c35e88@kernel.org
[ Rebased. Moved new variables above. Reworded title. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: tamird

rust/Makefile

@@ -117,6 +117,23 @@ syn-flags := \
     --extern quote \
     $(call cfgs-to-flags,$(syn-cfgs))
 
+pin_init_internal-cfgs := \
+    kernel
+
+pin_init_internal-flags := \
+    --extern proc_macro2 \
+    --extern quote \
+    --extern syn \
+    $(call cfgs-to-flags,$(pin_init_internal-cfgs))
+
+pin_init-cfgs := \
+    kernel
+
+pin_init-flags := \
+    --extern pin_init_internal \
+    --extern macros \
+    $(call cfgs-to-flags,$(pin_init-cfgs))
+
 # `rustdoc` did not save the target modifiers, thus workaround for
 # the time being (https://github.com/rust-lang/rust/issues/144521).
 rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
@@ -211,16 +228,15 @@ rustdoc-ffi: $(src)/ffi.rs rustdoc-core FORCE
 	+$(call if_changed,rustdoc)
 
 rustdoc-pin_init_internal: private rustdoc_host = yes
-rustdoc-pin_init_internal: private rustc_target_flags = --cfg kernel \
-    --extern proc_macro --extern proc_macro2 --extern quote --extern syn \
-    --crate-type proc-macro
+rustdoc-pin_init_internal: private rustc_target_flags = $(pin_init_internal-flags) \
+    --extern proc_macro --crate-type proc-macro
 rustdoc-pin_init_internal: $(src)/pin-init/internal/src/lib.rs \
     rustdoc-clean rustdoc-proc_macro2 rustdoc-quote rustdoc-syn FORCE
 	+$(call if_changed,rustdoc)
 
 rustdoc-pin_init: private rustdoc_host = yes
-rustdoc-pin_init: private rustc_target_flags = --extern pin_init_internal \
-    --extern macros --extern alloc --cfg kernel --cfg feature=\"alloc\"
+rustdoc-pin_init: private rustc_target_flags = $(pin_init-flags) \
+    --extern alloc --cfg feature=\"alloc\"
 rustdoc-pin_init: $(src)/pin-init/src/lib.rs rustdoc-pin_init_internal \
     rustdoc-macros FORCE
 	+$(call if_changed,rustdoc)
@@ -273,15 +289,14 @@ rusttestlib-macros: $(src)/macros/lib.rs \
     rusttestlib-proc_macro2 rusttestlib-quote rusttestlib-syn FORCE
 	+$(call if_changed,rustc_test_library)
 
-rusttestlib-pin_init_internal: private rustc_target_flags = --cfg kernel \
-    --extern proc_macro --extern proc_macro2 --extern quote --extern syn
+rusttestlib-pin_init_internal: private rustc_target_flags = $(pin_init_internal-flags) \
+    --extern proc_macro
 rusttestlib-pin_init_internal: private rustc_test_library_proc = yes
 rusttestlib-pin_init_internal: $(src)/pin-init/internal/src/lib.rs \
     rusttestlib-proc_macro2 rusttestlib-quote rusttestlib-syn FORCE
 	+$(call if_changed,rustc_test_library)
 
-rusttestlib-pin_init: private rustc_target_flags = --extern pin_init_internal \
-    --extern macros --cfg kernel
+rusttestlib-pin_init: private rustc_target_flags = $(pin_init-flags)
 rusttestlib-pin_init: $(src)/pin-init/src/lib.rs rusttestlib-macros \
     rusttestlib-pin_init_internal $(obj)/$(libpin_init_internal_name) FORCE
 	+$(call if_changed,rustc_test_library)
@@ -549,8 +564,7 @@ $(obj)/$(libmacros_name): $(src)/macros/lib.rs $(obj)/libproc_macro2.rlib \
     $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE
 	+$(call if_changed_dep,rustc_procmacro)
 
-$(obj)/$(libpin_init_internal_name): private rustc_target_flags = --cfg kernel \
-    --extern proc_macro2 --extern quote --extern syn
+$(obj)/$(libpin_init_internal_name): private rustc_target_flags = $(pin_init_internal-flags)
 $(obj)/$(libpin_init_internal_name): $(src)/pin-init/internal/src/lib.rs \
     $(obj)/libproc_macro2.rlib $(obj)/libquote.rlib $(obj)/libsyn.rlib FORCE
 	+$(call if_changed_dep,rustc_procmacro)
@@ -646,8 +660,7 @@ $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
 $(obj)/pin_init.o: private skip_gendwarfksyms = 1
-$(obj)/pin_init.o: private rustc_target_flags = --extern pin_init_internal \
-    --extern macros --cfg kernel
+$(obj)/pin_init.o: private rustc_target_flags = $(pin_init-flags)
 $(obj)/pin_init.o: $(src)/pin-init/src/lib.rs $(obj)/compiler_builtins.o \
     $(obj)/$(libpin_init_internal_name) $(obj)/$(libmacros_name) FORCE
 	+$(call if_changed_rule,rustc_library)