wasm: add a webassembly compiler backend, based on using binaryen (#17368)

examples/wasm/functions.v

@@ -0,0 +1,57 @@
+// `pub` functions will be exported.
+//
+// ```
+// v -b wasm -no-builtin functions.v
+// wasmer functions.wasm -i main.powi <a> <b>
+// wasmer functions.wasm -i main.gcd <a> <b>
+// ```
+
+pub fn gcd(a_ i64, b_ i64) i64 {
+	mut a := a_
+	mut b := b_
+	if a < 0 {
+		a = -a
+	}
+	if b < 0 {
+		b = -b
+	}
+	for b != 0 {
+		a %= b
+		if a == 0 {
+			return b
+		}
+		b %= a
+	}
+	return a
+}
+
+pub fn powi(a i64, b i64) i64 {
+	mut b_ := b
+	mut p := a
+	mut v := i64(1)
+
+	if b_ < 0 { // exponent < 0
+		if a == 0 {
+			return -1 // division by 0
+		}
+		return if a * a != 1 {
+			0
+		} else {
+			if (b_ & 1) > 0 {
+				a
+			} else {
+				1
+			}
+		}
+	}
+
+	for b_ > 0 {
+		if b_ & 1 > 0 {
+			v *= p
+		}
+		p *= p
+		b_ >>= 1
+	}
+
+	return v
+}