wasm: compile .c files in packages

targets/wasm.json

@@ -1,7 +1,12 @@
 {
 	"llvm-target":   "wasm32-unknown-unknown-wasm",
 	"build-tags":    ["js", "wasm"],
+	"compiler":      "clang-7",
 	"linker":        "ld.lld-7",
+	"cflags": [
+		"--target=wasm32",
+		"-Oz"
+	],
 	"ldflags": [
 		"-flavor", "wasm",
 		"-allow-undefined"