Un-revert "[Driver] Add -fdiagnostics-hotness-threshold"

Summary:
Un-revert https://reviews.llvm.org/D34868, but with a slight tweak to the
documentation to fix an error -- I had used the wrong syntax for a link.

llvm-svn: 306948
diff --git a/clang/lib/Frontend/CompilerInvocation.cpp b/clang/lib/Frontend/CompilerInvocation.cpp
index b1b10dd..5851595 100644
--- a/clang/lib/Frontend/CompilerInvocation.cpp
+++ b/clang/lib/Frontend/CompilerInvocation.cpp
@@ -909,12 +909,18 @@
   Opts.DiagnosticsWithHotness =
       Args.hasArg(options::OPT_fdiagnostics_show_hotness);
   bool UsingSampleProfile = !Opts.SampleProfileFile.empty();
+  bool UsingProfile = UsingSampleProfile ||
+      (Opts.getProfileUse() != CodeGenOptions::ProfileNone);
 
-  if (Opts.DiagnosticsWithHotness &&
-      Opts.getProfileUse() == CodeGenOptions::ProfileNone &&
-      !UsingSampleProfile) {
-    Diags.Report(diag::warn_drv_fdiagnostics_show_hotness_requires_pgo);
-  }
+  if (Opts.DiagnosticsWithHotness && !UsingProfile)
+    Diags.Report(diag::warn_drv_diagnostics_hotness_requires_pgo)
+        << "-fdiagnostics-show-hotness";
+
+  Opts.DiagnosticsHotnessThreshold = getLastArgUInt64Value(
+      Args, options::OPT_fdiagnostics_hotness_threshold_EQ, 0);
+  if (Opts.DiagnosticsHotnessThreshold > 0 && !UsingProfile)
+    Diags.Report(diag::warn_drv_diagnostics_hotness_requires_pgo)
+        << "-fdiagnostics-hotness-threshold=";
 
   // If the user requested to use a sample profile for PGO, then the
   // backend will need to track source location information so the profile