Improve depfile generation for rustc.

Author: graydon

src/Makefile

@@ -848,14 +848,17 @@ ifneq ($(RUSTBOOT_PROBE),)
 CFG_INFO := $(info cfg: using built $(CFG_BOOT) for rust deps)
 STDLIB_DEPFILE := $(CFG_STDLIB).d
 RUSTC_DEPFILE := $(CFG_RUSTC).d
-CRATE_DEPFILES := $(ALL_TEST_CRATES:%.rc=%.d) $(STDLIB_DEPFILE)
+CRATE_DEPFILES := $(ALL_TEST_CRATES:%.rc=%.d) \
+                  $(STDLIB_DEPFILE) \
+                  $(RUSTC_DEPFILE)
 
 $(STDLIB_DEPFILE): $(STDLIB_CRATE) $(MKFILES) $(CFG_BOOT) $(STDLIB_INPUTS)
 	@$(call CFG_ECHO, dep: $<)
 	$(BOOT) -shared -rdeps $< $(CFG_PATH_MUNGE) >$@.tmp \
     && mv [email protected] $@
 
-$(RUSTC_DEPFILE): $(STDLIB_CRATE) $(MKFILES) $(CFG_BOOT) $(COMPILER_INPUTS)
+$(RUSTC_DEPFILE): $(COMPILER_CRATE) $(COMPILER_INPUTS) \
+  $(STDLIB_CRATE) $(MKFILES) $(CFG_BOOT)
 	@$(call CFG_ECHO, dep: $<)
 	$(BOOT) -shared -rdeps $< $(CFG_PATH_MUNGE) >[email protected] \
     && mv [email protected] $@