compiler: die immediately instead of handling unknown target codegen

We cannot produce anything useful if asked to compile unknown targets.
We should handle the error immediately at the point of discovery instead
of propagating it upward, and preferably in the simplest way: Die.

This allows cleaning up our "error-handling" spread across 5 crates.

compiler/rustc_const_eval/src/errors.rs

@@ -16,7 +16,6 @@ use rustc_middle::mir::interpret::{
 };
 use rustc_middle::ty::{self, Mutability, Ty};
 use rustc_span::{Span, Symbol};
-use rustc_target::callconv::AdjustForForeignAbiError;
 
 use crate::interpret::InternKind;
 
@@ -936,9 +935,6 @@ impl<'tcx> ReportErrorExt for InvalidProgramInfo<'tcx> {
             InvalidProgramInfo::TooGeneric => const_eval_too_generic,
             InvalidProgramInfo::AlreadyReported(_) => const_eval_already_reported,
             InvalidProgramInfo::Layout(e) => e.diagnostic_message(),
-            InvalidProgramInfo::FnAbiAdjustForForeignAbi(_) => {
-                rustc_middle::error::middle_adjust_for_foreign_abi_error
-            }
         }
     }
     fn add_args<G: EmissionGuarantee>(self, diag: &mut Diag<'_, G>) {
@@ -953,12 +949,6 @@ impl<'tcx> ReportErrorExt for InvalidProgramInfo<'tcx> {
                 }
                 dummy_diag.cancel();
             }
-            InvalidProgramInfo::FnAbiAdjustForForeignAbi(
-                AdjustForForeignAbiError::Unsupported { arch, abi },
-            ) => {
-                diag.arg("arch", arch);
-                diag.arg("abi", abi.name());
-            }
         }
     }
 }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -106,9 +106,6 @@ impl<'tcx, M: Machine<'tcx>> FnAbiOfHelpers<'tcx> for InterpCx<'tcx, M> {
     ) -> InterpErrorKind<'tcx> {
         match err {
             FnAbiError::Layout(err) => err_inval!(Layout(err)),
-            FnAbiError::AdjustForForeignAbi(err) => {
-                err_inval!(FnAbiAdjustForForeignAbi(err))
-            }
         }
     }
 }