Use same toolchain throughout pgo+bolt build (JuliaLang#55460)

Also, I added the pgo flags to the `finish_stage2` target in case they
are or become useful there.

contrib/pgo-lto-bolt/Makefile

@@ -83,7 +83,7 @@ TOOLCHAIN_FLAGS = $\
 	"RANLIB=$(STAGE0_TOOLS)llvm-ranlib" $\
 	"CFLAGS+=$(PGO_CFLAGS)" $\
 	"CXXFLAGS+=$(PGO_CXXFLAGS)" $\
-	"LDFLAGS+=$(PGO_LDFLAGS)"
+	"LDFLAGS+=-fuse-ld=lld $(PGO_LDFLAGS)"
 
 $(STAGE0_BUILD) $(STAGE1_BUILD) $(STAGE2_BUILD):
 	$(MAKE) -C $(JULIA_ROOT) O=$@ configure
@@ -99,15 +99,15 @@ stage0: | $(STAGE0_BUILD)
 $(STAGE1_BUILD): stage0
 stage1: PGO_CFLAGS:=-fprofile-generate=$(PGO_PROFILE_DIR) -Xclang -mllvm -Xclang -vp-counters-per-site=$(COUNTERS_PER_SITE)
 stage1: PGO_CXXFLAGS:=-fprofile-generate=$(PGO_PROFILE_DIR) -Xclang -mllvm -Xclang -vp-counters-per-site=$(COUNTERS_PER_SITE)
-stage1: PGO_LDFLAGS:=-fuse-ld=lld -flto=thin -fprofile-generate=$(PGO_PROFILE_DIR)
+stage1: PGO_LDFLAGS:=-flto=thin -fprofile-generate=$(PGO_PROFILE_DIR)
 stage1: export USE_BINARYBUILDER_LLVM=0
 stage1: | $(STAGE1_BUILD)
 	$(MAKE) -C $(STAGE1_BUILD) $(TOOLCHAIN_FLAGS) && touch $@
 	@echo $(AFTER_STAGE1_MESSAGE)
 
 stage2: PGO_CFLAGS:=-fprofile-use=$(PGO_PROFILE_FILE)
 stage2: PGO_CXXFLAGS:=-fprofile-use=$(PGO_PROFILE_FILE)
-stage2: PGO_LDFLAGS:=-fuse-ld=lld -flto=thin -fprofile-use=$(PGO_PROFILE_FILE) -Wl,--icf=safe
+stage2: PGO_LDFLAGS:=-flto=thin -fprofile-use=$(PGO_PROFILE_FILE) -Wl,--icf=safe
 stage2: export USE_BINARYBUILDER_LLVM=0
 stage2: $(PGO_PROFILE_FILE) | $(STAGE2_BUILD)
 	$(MAKE) -C $(STAGE2_BUILD) $(TOOLCHAIN_FLAGS) $(BOLT_FLAGS) julia-src-release julia-symlink julia-libccalltest \
@@ -135,10 +135,13 @@ bolt_instrument: copy_originals
 
 # We don't want to rebuild julia-src as then we lose the bolt instrumentation
 # So we have to manually build the sysimage and package image
+finish_stage2: PGO_CFLAGS:=-fprofile-use=$(PGO_PROFILE_FILE)
+finish_stage2: PGO_CXXFLAGS:=-fprofile-use=$(PGO_PROFILE_FILE)
+finish_stage2: PGO_LDFLAGS:=-flto=thin -fprofile-use=$(PGO_PROFILE_FILE) -Wl,--icf=safe
 finish_stage2: stage2
-	$(MAKE) -C $(STAGE2_BUILD) julia-base-cache && \
-	$(MAKE) -C $(STAGE2_BUILD) -f sysimage.mk sysimg-release && \
-	$(MAKE) -C $(STAGE2_BUILD) -f pkgimage.mk release
+	$(MAKE) -C $(STAGE2_BUILD) $(TOOLCHAIN_FLAGS) julia-base-cache && \
+	$(MAKE) -C $(STAGE2_BUILD) $(TOOLCHAIN_FLAGS) -f sysimage.mk sysimg-release && \
+	$(MAKE) -C $(STAGE2_BUILD) $(TOOLCHAIN_FLAGS) -f pkgimage.mk release
 
 merge_data: bolt_instrument
 	for file in $(FILES_TO_OPTIMIZE); do \