Ensure non-null ProfileSummaryInfo passed to ModuleSummaryIndex builder

This fixes a ubsan bot failure after r302597, which made getProfileCount
non-static, but ended up invoking it on a null ProfileSummaryInfo object
in some cases from buildModuleSummaryIndex.

Most testing passed because the non-static getProfileCount currently
doesn't access any member variables, but I found this when testing a
follow on patch (D32877) that adds a member variable access.

llvm-svn: 302705

llvm/lib/Analysis/ModuleSummaryAnalysis.cpp

@@ -330,6 +330,7 @@ ModuleSummaryIndex llvm::buildModuleSummaryIndex(
     const Module &M,
     std::function<BlockFrequencyInfo *(const Function &F)> GetBFICallback,
     ProfileSummaryInfo *PSI) {
+  assert(PSI);
   ModuleSummaryIndex Index;
 
   // Identify the local values in the llvm.used and llvm.compiler.used sets,