[PGO] Adjust indirect call promotion threshold

[tejohnson]

Summary

Reduce min percent required for indirect call promotion from 33% to 30%,
which matches gcc's threshold and catches the same hot opportunities.

[davidxl]

this looks fine.

In the longer run, we should hook up the inline cost analysis with the icall promotion to compute the benefit of the promotion more quantitatively -- which can allow bumping down the threshold adaptively.

lib/Analysis/IndirectCallPromotionAnalysis.cpp

static cl::opt<unsigned>
     ICPCountThreshold("icp-count-threshold", cl::Hidden, cl::ZeroOrMore,
                       cl::init(1000),
                       cl::desc("The minimum count to the direct call target "
                                "for the promotion"));
 
 // The percent threshold for the direct-call target (this call site vs the
 // total call count) for it to be considered as the promotion target.
 static cl::opt<unsigned>
-    ICPPercentThreshold("icp-percent-threshold", cl::init(33), cl::Hidden,
+    ICPPercentThreshold("icp-percent-threshold", cl::init(30), cl::Hidden,
                         cl::ZeroOrMore,
                         cl::desc("The percentage threshold for the promotion"));
 
 // Set the maximum number of targets to promote for a single indirect-call
 // callsite.
 static cl::opt<unsigned>
     MaxNumPromotions("icp-max-prom", cl::init(2), cl::Hidden, cl::ZeroOrMore,
                      cl::desc("Max number of promotions for a single indirect "