stage2: remove use of builtin.stage2_arch workaround

The LLVM backend no longer needs this hack! However, the other backends
still do. So there are still some traces of this workaround in use for now.

lib/std/special/compiler_rt.zig

@@ -2,7 +2,7 @@ const std = @import("std");
 const builtin = @import("builtin");
 const is_test = builtin.is_test;
 const os_tag = builtin.os.tag;
-const arch = builtin.stage2_arch;
+const arch = builtin.cpu.arch;
 const abi = builtin.abi;
 
 const is_gnu = abi.isGnu();

src/Sema.zig

@@ -10186,7 +10186,7 @@ fn validateVarType(
     is_extern: bool,
 ) CompileError!void {
     var ty = var_ty;
-    const ok: bool = while (true) switch (ty.zigTypeTag()) {
+    while (true) switch (ty.zigTypeTag()) {
         .Bool,
         .Int,
         .Float,
@@ -10194,7 +10194,7 @@ fn validateVarType(
         .Enum,
         .Frame,
         .AnyFrame,
-        => break true,
+        => return,
 
         .BoundFn,
         .ComptimeFloat,
@@ -10205,14 +10205,14 @@ fn validateVarType(
         .Void,
         .Undefined,
         .Null,
-        => break false,
+        => break,
 
         .Pointer => {
             const elem_ty = ty.childType();
             if (elem_ty.zigTypeTag() == .Opaque) return;
             ty = elem_ty;
         },
-        .Opaque => break is_extern,
+        .Opaque => if (is_extern) return else break,
 
         .Optional => {
             var buf: Type.Payload.ElemType = undefined;
@@ -10223,15 +10223,17 @@ fn validateVarType(
 
         .ErrorUnion => ty = ty.errorUnionPayload(),
 
-        .Fn => @panic("TODO fn validateVarType"),
-        .Struct, .Union => {
+        .Fn, .Struct, .Union => {
             const resolved_ty = try sema.resolveTypeFields(block, src, ty);
-            break !resolved_ty.requiresComptime();
+            if (resolved_ty.requiresComptime()) {
+                break;
+            } else {
+                return;
+            }
         },
     } else unreachable; // TODO should not need else unreachable
-    if (!ok) {
-        return sema.fail(block, src, "variable of type '{}' must be const or comptime", .{var_ty});
-    }
+
+    return sema.fail(block, src, "variable of type '{}' must be const or comptime", .{var_ty});
 }
 
 pub const PanicId = enum {
@@ -11273,7 +11275,12 @@ fn coerce(
 
     const in_memory_result = coerceInMemoryAllowed(dest_type, inst_ty, false, target);
     if (in_memory_result == .ok) {
-        return sema.bitCast(block, dest_type, inst, inst_src);
+        if (try sema.resolveMaybeUndefVal(block, inst_src, inst)) |val| {
+            // Keep the comptime Value representation; take the new type.
+            return sema.addConstant(dest_type, val);
+        }
+        try sema.requireRuntimeBlock(block, inst_src);
+        return block.addTyOp(.bitcast, dest_type, inst);
     }
 
     // undefined to anything

src/type.zig

@@ -1458,7 +1458,7 @@ pub const Type = extern union {
                 }
             },
             .union_tagged => {
-                const union_obj = self.castTag(.@"union").?.data;
+                const union_obj = self.castTag(.union_tagged).?.data;
                 if (union_obj.tag_ty.hasCodeGenBits()) {
                     return true;
                 }
@@ -1470,7 +1470,6 @@ pub const Type = extern union {
                 }
             },
 
-            // TODO lazy types
             .array, .vector => self.elemType().hasCodeGenBits() and self.arrayLen() != 0,
             .array_u8 => self.arrayLen() != 0,
 

test/behavior/atomics.zig

@@ -89,7 +89,7 @@ test "128-bit cmpxchg" {
 
 fn test_u128_cmpxchg() !void {
     if (builtin.zig_is_stage2) {
-        if (builtin.stage2_arch != .x86_64) return error.SkipZigTest;
+        if (builtin.cpu.arch != .x86_64) return error.SkipZigTest;
         if (!builtin.stage2_x86_cx16) return error.SkipZigTest;
     } else {
         if (builtin.cpu.arch != .x86_64) return error.SkipZigTest;

test/behavior/widening.zig

@@ -30,8 +30,8 @@ test "float widening" {
 
 test "float widening f16 to f128" {
     // TODO https://github.com/ziglang/zig/issues/3282
-    if (@import("builtin").stage2_arch == .aarch64) return error.SkipZigTest;
-    if (@import("builtin").stage2_arch == .powerpc64le) return error.SkipZigTest;
+    if (@import("builtin").cpu.arch == .aarch64) return error.SkipZigTest;
+    if (@import("builtin").cpu.arch == .powerpc64le) return error.SkipZigTest;
 
     var x: f16 = 12.34;
     var y: f128 = x;