all: migrate code to new cast builtin syntax

Most of this migration was performed automatically with `zig fmt`. There
were a few exceptions which I had to manually fix:

* `@alignCast` and `@addrSpaceCast` cannot be automatically rewritten
* `@truncate`'s fixup is incorrect for vectors
* Test cases are not formatted, and their error locations change

tools/update-linux-headers.zig

@@ -112,7 +112,7 @@ const DestTarget = struct {
             _ = self;
             var hasher = std.hash.Wyhash.init(0);
             std.hash.autoHash(&hasher, a.arch);
-            return @truncate(u32, hasher.final());
+            return @as(u32, @truncate(hasher.final()));
         }
 
         pub fn eql(self: @This(), a: DestTarget, b: DestTarget, b_index: usize) bool {