make it possible to use snapshot core lib

mk/target.mk

@@ -4,10 +4,12 @@
 # $(2) is the target triple
 # $(3) is the host triple
 
-# If you are making non-backwards compatible changes to the runtime,
-# set this flag to 1.  It will cause stage1 to use the snapshot
-# runtime rather than the runtime from the working directory.
+# If you are making non-backwards compatible changes to the runtime
+# (resp.  corelib), set this flag to 1.  It will cause stage1 to use
+# the snapshot runtime (resp. corelib) rather than the runtime
+# (resp. corelib) from the working directory.
 USE_SNAPSHOT_RUNTIME=0
+USE_SNAPSHOT_CORELIB=0
 
 # Do not use --enforce-mut-vars in stage0, for now, as the snapshot
 # has an older version of the check.
@@ -34,15 +36,9 @@ $$(TLIB$(1)_T_$(2)_H_$(3))/libmorestack.a: \
 	@$$(call E, cp: $$@)
 	$$(Q)cp $$< $$@
 
-$$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_CORELIB): \
-		$$(CORELIB_CRATE) $$(CORELIB_INPUTS) \
-		$$(TSREQ$(1)_T_$(2)_H_$(3))
-	@$$(call E, compile_and_link: $$@)
-	$$(STAGE$(1)_T_$(2)_H_$(3)) --enforce-mut-vars -o $$@ $$< && touch $$@
-
 $$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_STDLIB): \
 		$$(STDLIB_CRATE) $$(STDLIB_INPUTS) \
-        $$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_CORELIB) \
+	        $$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_CORELIB) \
 		$$(TSREQ$(1)_T_$(2)_H_$(3))
 	@$$(call E, compile_and_link: $$@)
 	$$(STAGE$(1)_T_$(2)_H_$(3)) $$(ENFORCE_MUT_VARS_$(1)) \
@@ -107,9 +103,35 @@ $$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_RUNTIME): \
 
 endef
 
+# As above, but builds the corelib either by taking it out of the
+# snapshot or from the working directory.
+
+define TARGET_CORELIB_FROM_SNAPSHOT
+
+$$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_CORELIB): \
+		$$(HLIB$(1)_H_$(3))/$$(CFG_CORELIB) \
+		$$(CORELIB_INPUTS) \
+		$$(TSREQ$(1)_T_$(2)_H_$(3))
+	@$$(call E, cp: $$@)
+	$$(Q)cp $$< $$@
+	$$(Q)cp $$(HLIB$(1)_H_$(3))/$$(CORELIB_GLOB) \
+		$$(TLIB$(1)_T_$(2)_H_$(3))
+
+endef
+
+define TARGET_CORELIB_FROM_WD
+
+$$(TLIB$(1)_T_$(2)_H_$(3))/$$(CFG_CORELIB): \
+		$$(CORELIB_CRATE) $$(CORELIB_INPUTS) \
+		$$(TSREQ$(1)_T_$(2)_H_$(3))
+	@$$(call E, compile_and_link: $$@)
+	$$(STAGE$(1)_T_$(2)_H_$(3)) --enforce-mut-vars -o $$@ $$< && touch $$@
+
+endef
+
 # In principle, each host can build each target:
-$(foreach source,$(CFG_TARGET_TRIPLES),						\
- $(foreach target,$(CFG_TARGET_TRIPLES),					\
+$(foreach source,$(CFG_TARGET_TRIPLES),				\
+ $(foreach target,$(CFG_TARGET_TRIPLES),			\
   $(eval $(call TARGET_STAGE_N,0,$(target),$(source)))		\
   $(eval $(call TARGET_STAGE_N,1,$(target),$(source)))		\
   $(eval $(call TARGET_STAGE_N,2,$(target),$(source)))		\
@@ -125,15 +147,27 @@ else
 		$(eval $(call TARGET_RT_FROM_WD,0,$(src),$(src))))
 endif
 
+ifeq ($(USE_SNAPSHOT_CORELIB),1)
+    $(foreach src,$(CFG_HOST_TRIPLE),\
+		$(eval $(call TARGET_CORELIB_FROM_SNAPSHOT,0,$(src),$(src))))
+else 
+    $(foreach src,$(CFG_HOST_TRIPLE),\
+		$(eval $(call TARGET_CORELIB_FROM_WD,0,$(src),$(src))))
+endif
+
 # Non-host triples build the stage0 runtime from the working directory
-$(foreach source,$(CFG_TARGET_TRIPLES),						\
- $(foreach target,$(NON_HOST_TRIPLES),					\
+$(foreach source,$(CFG_TARGET_TRIPLES),				\
+ $(foreach target,$(NON_HOST_TRIPLES),				\
   $(eval $(call TARGET_RT_FROM_WD,0,$(target),$(source)))))
 
 # After stage0, always build the stage0 runtime from the working directory
-$(foreach source,$(CFG_TARGET_TRIPLES),						\
- $(foreach target,$(CFG_TARGET_TRIPLES),					\
+$(foreach source,$(CFG_TARGET_TRIPLES),				\
+ $(foreach target,$(CFG_TARGET_TRIPLES),			\
   $(eval $(call TARGET_RT_FROM_WD,1,$(target),$(source)))	\
   $(eval $(call TARGET_RT_FROM_WD,2,$(target),$(source)))	\
-  $(eval $(call TARGET_RT_FROM_WD,3,$(target),$(source)))))
+  $(eval $(call TARGET_RT_FROM_WD,3,$(target),$(source)))  	\
+  $(eval $(call TARGET_CORELIB_FROM_WD,1,$(target),$(source)))	\
+  $(eval $(call TARGET_CORELIB_FROM_WD,2,$(target),$(source)))	\
+  $(eval $(call TARGET_CORELIB_FROM_WD,3,$(target),$(source)))	\
+))