Clean rust target when rustc bumped up

Fix:
```
error[E0514]: found crate `jit` compiled by an incompatible version of rustc
```

Author: nobu

defs/jit.mk

@@ -22,7 +22,7 @@ RUST_LIB_TOUCH = touch $@
 #    ld: warning: object file (target/debug/libjit.a(<libcapstone object>)) was built for
 #    newer macOS version (15.2) than being linked (15.0)
 # This limits us to an older set of macOS API in the rust code, but we don't use any.
-$(RUST_LIB): $(srcdir)/ruby.rs
+$(RUST_LIB): $(srcdir)/ruby.rs target/.rustc-version
 	$(Q)if [ '$(ZJIT_SUPPORT)' != no -a '$(YJIT_SUPPORT)' != no ]; then \
 	    echo 'building YJIT and ZJIT ($(JIT_CARGO_SUPPORT:yes=release) mode)'; \
 	elif [ '$(ZJIT_SUPPORT)' != no ]; then \
@@ -37,7 +37,7 @@ $(RUST_LIB): $(srcdir)/ruby.rs
 	$(RUST_LIB_TOUCH)
 else ifneq ($(strip $(RLIB_DIR)),) # combo build
 
-$(RUST_LIB): $(srcdir)/ruby.rs
+$(RUST_LIB): $(srcdir)/ruby.rs target/.rustc-version
 	$(ECHO) 'building $(@F)'
 	$(gnumake_recursive)$(Q) $(RUSTC) --edition=2024 \
 	    $(RUSTC_FLAGS) \
@@ -54,7 +54,7 @@ $(RUST_LIB): $(srcdir)/ruby.rs
 JIT_RLIB = $(TOP_BUILD_DIR)/$(RLIB_DIR)/libjit.rlib
 $(YJIT_RLIB): $(JIT_RLIB)
 $(ZJIT_RLIB): $(JIT_RLIB)
-$(JIT_RLIB):
+$(JIT_RLIB): target/.rustc-version
 	$(ECHO) 'building $(@F)'
 	$(gnumake_recursive)$(Q) $(RUSTC) --crate-name=jit \
 	    --edition=2024 \
@@ -77,6 +77,17 @@ endif
 rust-libobj: $(RUST_LIBOBJ)
 rust-lib: $(RUST_LIB)
 
+rustc-version-check: target/.rustc-version
+
+target/.rustc-version: PHONY
+	$(eval prev_version := $(if $(wildcard $@),$(shell cat $@)))
+	$(eval curr_version := $(shell $(RUSTC) -V | cut -d' ' -f2))
+	$(eval clean := $(filter-out $(prev_version),$(curr_version)))
+	$(if $(clean),$(ECHO) Cleaning $(@D) for rustc $(curr_version))
+	$(if $(clean),$(Q)$(RMALL) $(@D))
+	$(Q)$(MAKEDIRS) $(@D)
+	$(Q)echo $(curr_version) > $@
+
 # For Darwin only: a list of symbols that we want the glommed Rust static lib to export.
 # Unfortunately, using wildcard like '_rb_*' with -exported-symbol does not work, at least
 # not on version 820.1. Assume llvm-nm, so XCode 8.0 (from 2016) or newer.

yjit/yjit.mk

@@ -16,14 +16,14 @@ BUILD_YJIT_LIBS = $(TOP_BUILD_DIR)/$(YJIT_LIBS)
 # In a YJIT-only build (no ZJIT)
 ifneq ($(strip $(YJIT_LIBS)),)
 yjit-libs: $(BUILD_YJIT_LIBS)
-$(BUILD_YJIT_LIBS): $(YJIT_SRC_FILES)
+$(BUILD_YJIT_LIBS): $(YJIT_SRC_FILES) rustc-version-check
 	$(ECHO) 'building Rust YJIT (release mode)'
 	$(gnumake_recursive)$(Q) $(RUSTC) $(YJIT_RUSTC_ARGS)
 else ifneq ($(strip $(RLIB_DIR)),) # combo build
 # Absolute path to avoid VPATH ambiguity
 YJIT_RLIB = $(TOP_BUILD_DIR)/$(RLIB_DIR)/libyjit.rlib
 
-$(YJIT_RLIB): $(YJIT_SRC_FILES)
+$(YJIT_RLIB): $(YJIT_SRC_FILES) rustc-version-check
 	$(ECHO) 'building $(@F)'
 	$(gnumake_recursive)$(Q) $(RUSTC) '-L$(@D)' --extern=jit $(YJIT_RUSTC_ARGS)
 

zjit/zjit.mk

@@ -20,14 +20,14 @@ BUILD_ZJIT_LIBS = $(TOP_BUILD_DIR)/$(ZJIT_LIBS)
 
 # In a ZJIT-only build (no YJIT)
 ifneq ($(strip $(ZJIT_LIBS)),)
-$(BUILD_ZJIT_LIBS): $(ZJIT_SRC_FILES)
+$(BUILD_ZJIT_LIBS): $(ZJIT_SRC_FILES) rustc-version-check
 	$(ECHO) 'building Rust ZJIT (release mode)'
 	$(gnumake_recursive)$(Q) $(RUSTC) $(ZJIT_RUSTC_ARGS)
 else ifneq ($(strip $(RLIB_DIR)),) # combo build
 # Absolute path to avoid VPATH ambiguity
 ZJIT_RLIB = $(TOP_BUILD_DIR)/$(RLIB_DIR)/libzjit.rlib
 
-$(ZJIT_RLIB): $(ZJIT_SRC_FILES)
+$(ZJIT_RLIB): $(ZJIT_SRC_FILES) rustc-version-check
 	$(ECHO) 'building $(@F)'
 	$(gnumake_recursive)$(Q) $(RUSTC) '-L$(@D)' --extern=jit $(ZJIT_RUSTC_ARGS)