tests: Adopt ABI transmute tests from crashtests

tests/auxiliary/minicore.rs

@@ -16,6 +16,7 @@
 
 #![feature(
     no_core,
+    intrinsics,
     lang_items,
     auto_traits,
     freeze_impls,
@@ -196,3 +197,9 @@ impl<'a, 'b: 'a, T: PointeeSized + Unsize<U>, U: PointeeSized> CoerceUnsized<&'a
 trait Drop {
     fn drop(&mut self);
 }
+
+pub mod mem {
+    #[rustc_nounwind]
+    #[rustc_intrinsic]
+    pub unsafe fn transmute<Src, Dst>(src: Src) -> Dst;
+}

tests/crashes/138738.rs

@@ -1,7 +0,0 @@
-//@ known-bug: #138738
-//@ only-x86_64
-
-#![feature(abi_ptx)]
-fn main() {
-    let a = unsafe { core::mem::transmute::<usize, extern "ptx-kernel" fn(i32)>(4) }(2);
-}

tests/ui/abi/unsupported-abi-transmute.rs

@@ -0,0 +1,15 @@
+//@ add-core-stubs
+//@ compile-flags: --crate-type=lib --target x86_64-unknown-none
+//@ needs-llvm-components: x86
+//@ edition: 2018
+#![no_core]
+#![feature(no_core, lang_items)]
+extern crate minicore;
+use minicore::*;
+
+// Check we error before unsupported ABIs reach codegen stages.
+
+fn anything() {
+    let a = unsafe { mem::transmute::<usize, extern "thiscall" fn(i32)>(4) }(2);
+    //~^ ERROR: is not a supported ABI for the current target [E0570]
+}

tests/ui/abi/unsupported-abi-transmute.stderr

@@ -0,0 +1,9 @@
+error[E0570]: "thiscall" is not a supported ABI for the current target
+  --> $DIR/unsupported-abi-transmute.rs:13:53
+   |
+LL |     let a = unsafe { mem::transmute::<usize, extern "thiscall" fn(i32)>(4) }(2);
+   |                                                     ^^^^^^^^^^
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0570`.