Updated GDC Explorer site (gdc-9.1)

[Iain Buclaw]

Hi,

Another year, another site update.  This syncs with the latest 
gcc-explorer, and refreshes all compilers to version 9.1.

This time around, I've built 190 (one-hundred-and-ninety) D 
compilers, each for a different target configuration, and dropped 
all the old unofficial versions from the list.

Platform support is quite thin, so using phobos/druntime won't 
work with a lot of them.  The primary OS targets are expected to 
be sorted out in time for version 9.2.

https://explore.dgnu.org/

Regards,
Iain.