Use zig to build bitcode

compiler/builtins/bitcode/src/main.zig

@@ -0,0 +1,18 @@
+const std = @import("std");
+const testing = std.testing;
+
+fn is_finite_(f: f64) bool {
+    return std.math.isFinite(f);
+}
+
+fn atan(f: f64) f64 {
+    return std.math.atan(f);
+}
+
+fn pow_int_(base: i64, exp: i64) i64 {
+    return std.math.pow(i64, base, exp);
+}
+
+// test "basic add functionality" {
+    // testing.expect(add(3, 7) == 10);
+// }