Add new platforms strings to PlatformInfo
As discussed at the Core Software Meeting the platforms we will use for LCG 100 should be
- x86_64_v2-centos7-gcc9-opt
- x86_64_v2-centos7-gcc9-dbg
- x86_64_v2-centos7-gcc9-do0
- x86_64_v3-centos7-gcc9-opt
- x86_64_v4+vecwid256-centos7-gcc9-opt
- x86_64_v2-centos7-gcc10-opt
- x86_64_v2-centos7-gcc10-dbg
- x86_64_v2-centos7-clang11-opt
- x86_64_v2-centos7-clang11-dbg
with the possibility of adding
- x86_64_v2-centos7-gcc10-do0
- x86_64_v3-centos7-gcc10-opt
- x86_64_v4+vecwid256-centos7-gcc10-opt
This MR adds all the foreseen platforms to the PlatformInfo list.