Remove reference to LoopVectorization in PGO Makefile (#54175)

Noting that the profile counters aren't atomic seems useful so I threw
that in as well.

Author: Zentrik

contrib/pgo-lto/Makefile

@@ -18,12 +18,12 @@ LLVM_OBJCOPY:=$(STAGE0_TOOLS)llvm-objcopy
 # When building a single libLLVM.so we need to increase -vp-counters-per-site
 # significantly
 COUNTERS_PER_SITE:=6
+# Note: profile counters are not atomic by default, https://discourse.llvm.org/t/profile-guided-optimization-pgo-related-questions-and-suggestions/75232/5
 
-AFTER_STAGE1_MESSAGE:='Run `make clean-profiles` to start with a clean slate. $\
-    Then run Julia to collect realistic profile data, for example: `$(STAGE1_BUILD)/julia -O3 -e $\
-    '\''using Pkg; Pkg.add("LoopVectorization"); Pkg.test("LoopVectorization")'\''`. This $\
-	should produce about 15MB of data in $(PROFILE_DIR). Note that running extensive $\
-	scripts may result in counter overflows, which can be detected by running $\
+AFTER_STAGE1_MESSAGE:='You can now optionally collect more profiling data for use in PGO by running Julia $\
+	with an appropriate workload. If you wish, run `make clean_profiles` before doing so to remove any profiling data $\
+	generated by building Julia. You should end up with about 15MB of data in $(PGO_PROFILE_DIR). $\
+	Note that running extensive scripts may result in counter overflows, which can be detected by running $\
 	`make top`. Afterwards run `make stage2`.'
 
 TOOLCHAIN_FLAGS = $\