x86_64: implement error set and enum safety

This is all of the expected 0.14.0 progress on #21530, which can now be
postponed once this commit is merged.

This required rewriting the (un)wrap operations since the original
implementations were extremely buggy.

Also adds an easy way to retrigger Sema OPV bugs so that I don't have to
keep updating #22419 all the time.

Author: jacobly0

src/Sema.zig

@@ -8850,7 +8850,7 @@ fn zirEnumFromInt(sema: *Sema, block: *Block, inst: Zir.Inst.Index) CompileError
             // Use `intCast`, since it'll set up the Sema-emitted safety checks for us!
             const int_val = try sema.intCast(block, src, int_tag_ty, src, operand, src, true, true);
             const result = try block.addBitCast(dest_ty, int_val);
-            if (zcu.backendSupportsFeature(.is_named_enum_value)) {
+            if (!dest_ty.isNonexhaustiveEnum(zcu) and zcu.backendSupportsFeature(.is_named_enum_value)) {
                 const ok = try block.addUnOp(.is_named_enum_value, result);
                 try sema.addSafetyCheck(block, src, ok, .invalid_enum_value);
             }

src/Type.zig

@@ -4190,11 +4190,11 @@ pub const @"c_longlong": Type = .{ .ip_index = .c_longlong_type };
 pub const @"c_ulonglong": Type = .{ .ip_index = .c_ulonglong_type };
 pub const @"c_longdouble": Type = .{ .ip_index = .c_longdouble_type };
 
-pub const slice_const_u8: Type = .{ .ip_index = .slice_const_u8_type };
 pub const manyptr_u8: Type = .{ .ip_index = .manyptr_u8_type };
-pub const single_const_pointer_to_comptime_int: Type = .{
-    .ip_index = .single_const_pointer_to_comptime_int_type,
-};
+pub const manyptr_const_u8: Type = .{ .ip_index = .manyptr_const_u8_type };
+pub const manyptr_const_u8_sentinel_0: Type = .{ .ip_index = .manyptr_const_u8_sentinel_0_type };
+pub const single_const_pointer_to_comptime_int: Type = .{ .ip_index = .single_const_pointer_to_comptime_int_type };
+pub const slice_const_u8: Type = .{ .ip_index = .slice_const_u8_type };
 pub const slice_const_u8_sentinel_0: Type = .{ .ip_index = .slice_const_u8_sentinel_0_type };
 
 pub const vector_16_i8: Type = .{ .ip_index = .vector_16_i8_type };