Also bump Linux Clang baseline to 12.0.1 (was: Bump --enable-compiler-plugins Clang baseline?)

[Stephan Bergmann]

This is all done now, 
<https://git.libreoffice.org/core/+/fe6043136fd3ba0333b99b8ca4dda699961c2bfd%5E%21> 
"Bump Linux Clang baseline to 8.0.1" and 
<https://git.libreoffice.org/core/+/d1a2b80b9dc146c7fe63d2657e5506f49d6e5c0d%5E%21> 
"Bump compiler plugins Clang baseline to 12.0.1".