Auto merge of #5086 - Areredify:issue-3746, r=phansch

don't fire `empty_loop` in `no_std` crates

closes #3746.
changelog: move no_std detection to utils, don't fire empty_loop in no_std crates

tests/ui/issue-3746.rs

@@ -0,0 +1,22 @@
+// ignore-macos
+// ignore-windows
+
+#![warn(clippy::empty_loop)]
+#![feature(lang_items, link_args, start, libc)]
+#![link_args = "-nostartfiles"]
+#![no_std]
+
+use core::panic::PanicInfo;
+
+#[start]
+fn main(argc: isize, argv: *const *const u8) -> isize {
+    loop {}
+}
+
+#[panic_handler]
+fn panic(_info: &PanicInfo) -> ! {
+    loop {}
+}
+
+#[lang = "eh_personality"]
+extern "C" fn eh_personality() {}