Switch "make all" to build stage2 versions of fuzzer, cargo, and rustdoc

This should trim some time off "make all" because it doesn't force the
stage3 rustc to be built. Even better, we can directly use the cargo out
of the build directory because we automatically build the stage2 libcore
and libstd.

Makefile.in

@@ -421,9 +421,9 @@ else
 TSREQS :=											\
 	$(foreach target,$(CFG_TARGET_TRIPLES),			\
 		$(SREQ3_T_$(target)_H_$(CFG_HOST_TRIPLE)))
-FUZZ := $(HBIN3_H_$(CFG_HOST_TRIPLE))/fuzzer$(X)
-CARGO := $(HBIN3_H_$(CFG_HOST_TRIPLE))/cargo$(X)
-RUSTDOC := $(HBIN3_H_$(CFG_HOST_TRIPLE))/rustdoc$(X)
+FUZZ := $(HBIN2_H_$(CFG_HOST_TRIPLE))/fuzzer$(X)
+CARGO := $(HBIN2_H_$(CFG_HOST_TRIPLE))/cargo$(X)
+RUSTDOC := $(HBIN2_H_$(CFG_HOST_TRIPLE))/rustdoc$(X)
 
 all: rustc $(GENERATED) docs $(FUZZ) $(CARGO) $(RUSTDOC)