[wasm][test] Skip crash tests on WASI for now

WASI doesn't support spawning a subprocess, so crash tests crashes the
test harness itself. Skip them for now.

Author: kateinoigakukun

test/stdlib/UnsafePointer.swift.gyb

@@ -537,6 +537,7 @@ ${SelfName}TestSuite.test("pointer(to:)") {
 % end
 }
 
+#if !os(WASI)
 ${SelfName}TestSuite.test("pointer(to:).overflow") {
   struct Example {
     var a = false
@@ -558,6 +559,7 @@ ${SelfName}TestSuite.test("pointer(to:).overflow") {
   let doublePointer = p.pointer(to: \.d)
   expectNotNil(doublePointer)
 }
+#endif
 
 % end