Update determination of "too complex" expression to take time into account.

By default, end expression type checking after the elapsed process time
is more than 60 seconds for the current expression. This threshold can
be overridden by using -solver-expression-time-threshold=<seconds>.

Resolves rdar://problem/32859654

lib/Sema/ConstraintSystem.cpp

@@ -29,9 +29,7 @@ using namespace constraints;
 #define DEBUG_TYPE "ConstraintSystem"
 
 ExpressionTimer::~ExpressionTimer() {
-  llvm::TimeRecord endTime = llvm::TimeRecord::getCurrentTime(false);
-
-  auto elapsed = endTime.getProcessTime() - StartTime.getProcessTime();
+  auto elapsed = getElapsedProcessTimeInFractionalSeconds();
   unsigned elapsedMS = static_cast<unsigned>(elapsed * 1000);
 
   if (ShouldDump) {