Use cfg_if in libpanic_abort.

This allows setting a default abort using the core intrinsic.

Cargo.lock

@@ -2056,6 +2056,7 @@ dependencies = [
 name = "panic_abort"
 version = "0.0.0"
 dependencies = [
+ "cfg-if",
  "compiler_builtins",
  "core",
  "libc",

src/libpanic_abort/Cargo.toml

@@ -11,6 +11,7 @@ bench = false
 doc = false
 
 [dependencies]
+cfg-if = { version = "0.1.8", features = ['rustc-dep-of-std'] }
 core = { path = "../libcore" }
 libc = { version = "0.2", default-features = false }
 compiler_builtins = "0.1.0"

src/libpanic_abort/lib.rs

@@ -40,17 +40,13 @@ pub unsafe extern "C" fn __rust_panic_cleanup(_: *mut u8) -> *mut (dyn Any + Sen
 pub unsafe extern "C" fn __rust_start_panic(_payload: usize) -> u32 {
     abort();
 
-    #[cfg(any(unix, target_os = "cloudabi"))]
+    cfg_if::cfg_if! {
+        if #[cfg(any(unix, target_os = "cloudabi"))] {
             unsafe fn abort() -> ! {
                 libc::abort();
             }
-
+        } else if #[cfg(any(target_os = "hermit",
-    #[cfg(any(windows, all(target_arch = "wasm32", not(target_os = "emscripten"))))]
+                        all(target_vendor = "fortanix", target_env = "sgx")))] {
-    unsafe fn abort() -> ! {
-        core::intrinsics::abort();
-    }
-
-    #[cfg(any(target_os = "hermit", all(target_vendor = "fortanix", target_env = "sgx")))]
             unsafe fn abort() -> ! {
                 // call std::sys::abort_internal
                 extern "C" {
@@ -58,6 +54,12 @@ pub unsafe extern "C" fn __rust_start_panic(_payload: usize) -> u32 {
                 }
                 __rust_abort();
             }
+        } else {
+            unsafe fn abort() -> ! {
+                core::intrinsics::abort();
+            }
+        }
+    }
 }
 
 // This... is a bit of an oddity. The tl;dr; is that this is required to link