[Tests] NFC: Adjust scope threshold for rdar://rdar31742586 test-case

The test was slow with hacks but now it's much faster - takes about
63k scopes to solve, it could be improved by introducing new overloads
of prefix `-` to stdlib.

Author: xedin

validation-test/Sema/type_checker_perf/fast/rdar31742586.swift

@@ -0,0 +1,11 @@
+// RUN: %target-typecheck-verify-swift -solver-scope-threshold=1000
+// REQUIRES: tools-release,no_asan
+
+// The test takes about 63k scopes here due to the fact
+// that prefix `-` operator doesn't have an overload that
+// take `Int`. We could fix that in the stdlib.
+
+func rdar31742586() -> Double {
+  return -(1 + 2) + -(3 + 4) + 5 - (-(1 + 2) + -(3 + 4) + 5)
+  // expected-error@-1 {{the compiler is unable to type-check this expression in reasonable time}}
+}