The leading/trailing whitespace is problematic because of e.g.
`WHEN` macro having preceeding whitespace for alignment, and it is
generally messy.
Credits to Phil who did lot of the original work.
Closes#1708
The support is to be considered experimental, that is, the interfaces,
the first party generators and helper functions can change or be removed
at any point in time.
Related to #850
Swept:
`-Wpadded` in some places (where it caused extra size, instead of just
saying "hey, we padded struct at the end to align, just as standard says")
`-Wweak-vtables` everywhere (Clang)
`-Wexit-time-destructors` everywhere (Clang)
`-Wmissing-noreturn` everywhere (Clang)
The last three are enabled for Clang compilation going forward.
Also enabled `-Wunreachable-code` for Clang and GCC
