Fix test character_literals.swift. Requires 64-bit.

Author: atrick

test/SILOptimizer/character_literals.swift

@@ -1,6 +1,7 @@
 // RUN: %target-swift-frontend -parse-as-library -O -emit-ir  %s | %FileCheck %s
 // REQUIRES: swift_stdlib_no_asserts,optimized_stdlib
 // REQUIRES: swift_in_compiler
+// REQUIRES: PTRSIZE=64
 
 // This is an end-to-end test to ensure that the optimizer generates
 // a simple literal for character literals.