stage3 regression for comptime slice concat (need explicit comptime block)

minimized.zig

const std = @import("std");

fn sdk_root() []const u8 {
    return std.fs.path.dirname(@src().file) orelse ".";
}

fn dep_root_working() []const u8 {
    const sdk_root_val = comptime blk: { break :blk sdk_root(); };
    return sdk_root_val ++ "/deps/mpack";
}

fn dep_root_broken() []const u8 {
    return sdk_root() ++ "/deps/mpack";
}

pub fn main() !void {
    std.debug.print("{s}\n", .{dep_root_working()});
    std.debug.print("{s}\n", .{dep_root_broken()});
}