builtin.wasm_bare: fix malloc invocation (#13740)

vlib/builtin/wasm_bare/libc_impl.v

@@ -5,7 +5,7 @@ module builtin
 [unsafe]
 pub fn __malloc(size usize) voidptr {
 	unsafe {
-		return malloc(int(size))
+		return C.malloc(int(size))
 	}
 }