[WASM] Fix to build StdlibUnittest for WASM (#198)

Author: kateinoigakukun

stdlib/private/StdlibUnittest/StdlibUnittest.swift

@@ -811,8 +811,10 @@ var _testSuiteNameToIndex: [String : Int] = [:]
 let _stdlibUnittestStreamPrefix = "__STDLIB_UNITTEST__"
 let _crashedPrefix = "CRASHED:"
 
+#if !os(WASI)
 @_silgen_name("installTrapInterceptor")
 func _installTrapInterceptor()
+#endif
 
 #if _runtime(_ObjC)
 @objc protocol _StdlibUnittestNSException {
@@ -823,7 +825,9 @@ func _installTrapInterceptor()
 // Avoid serializing references to objc_setUncaughtExceptionHandler in SIL.
 @inline(never)
 func _childProcess() {
+#if !os(WASI)
   _installTrapInterceptor()
+#endif
 
 #if _runtime(_ObjC)
   objc_setUncaughtExceptionHandler {