Simplifying LibreOffice build instructions

[Stephan Bergmann]

On 02/06/2022 11:50, Hossein Nourikhah wrote:
> Build LibreOffice from source code
> https://wiki.documentfoundation.org/User:Hossein/Build

Some of the per-platform instructions make it sound like our JDK 
baseline is 11, while my understanding is that it is 9 in general (cf. 
<https://git.libreoffice.org/core/+/941b567a41569260fef14a7337511e8f42337323%5E!/> 
"tdf#131572 Add java 9 module info for libreoffice.jar") and 17 for 
macOS on Apple Silicon (cf. 
<https://lists.freedesktop.org/archives/libreoffice/2022-June/088977.html> 
"Re: Using Java on macOS ARM64").