Revert "[StackSafety,NFC] Remove unneded constexpr"

This reverts commit 38470ba because it
breaks builds with lld and gold linkers.

llvm/lib/IR/ModuleSummaryIndex.cpp

@@ -35,6 +35,8 @@ static cl::opt<bool> ImportConstantsWithRefs(
     "import-constants-with-refs", cl::init(true), cl::Hidden,
     cl::desc("Import constant global variables with references"));
 
+constexpr uint32_t FunctionSummary::ParamAccess::RangeWidth;
+
 FunctionSummary FunctionSummary::ExternalNode =
     FunctionSummary::makeDummyFunctionSummary({});