CMake: remove -Dstd-docs=false flag when building stage3
This now defaults to false already since the autodocs rework.
The langref still cannot be enabled by default because the langref
contains doctests that exercise the `@cImport` feature which is disabled
in zig2 builds.
0884a43411Andrew Kelley committed on 6/7/2024, 7:42:14 PMparentaab5ccc