[android] Force parsing of literal as unsigned.

0xffffffff do not fit into Int, and even if it doesn't, Swift
doesn't change the default to be UInt and fit, so we have to
be explicit.

Author: drodriguez

test/stdlib/Runtime.swift.gyb

@@ -560,7 +560,7 @@ Runtime.test("SwiftError layout constants for LLDB") {
   let RTLD_DEFAULT = UnsafeMutableRawPointer(bitPattern: 0)
 #elseif os(Android)
   #if arch(arm)
-    let RTLD_DEFAULT = UnsafeMutableRawPointer(bitPattern: 0xffffffff)
+    let RTLD_DEFAULT = UnsafeMutableRawPointer(bitPattern: 0xffffffff as UInt)
   #elseif arch(arm64)
     let RTLD_DEFAULT = UnsafeMutableRawPointer(bitPattern: 0)
   #else