[WASM] Initial infrastructure

- New module ":compiler:backend.wasm"
    - Initial compiler infra (driver, phaser, context)
    - Subset of Wasm AST
    - Skeleton of IR -> Wasm AST
    - Wasm AST -> WAT transformer

- Testing infra

- SpiderMonkey jsshell tool

libraries/stdlib/wasm/internal/WasmMath.kt

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2010-2019 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package kotlin.wasm.internal
+
+// `compareTo(x, y)` implemented as `(x >= y) - (x <= y)`
+
+fun wasm_i32_compareTo(x: Int, y: Int): Int =
+    wasm_i32_ge_s(x, y) - wasm_i32_le_s(x, y)
+
+fun wasm_i64_compareTo(x: Long, y: Long): Int =
+    wasm_i64_ge_s(x, y) - wasm_i64_le_s(x, y)
+
+fun wasm_f32_compareTo(x: Float, y: Float): Int =
+    wasm_f32_ge(x, y) - wasm_f32_le(x, y)
+
+fun wasm_f64_compareTo(x: Double, y: Double): Int =
+    wasm_f64_ge(x, y) - wasm_f64_le(x, y)