Auto merge of #111819 - nikarh:vita-improved, r=Amanieu

Improved std support for ps vita target

Fixed a couple of things in std support for ps vita via Vita SDK newlib oss implementation:

- Added missing hardware features to target spec
- Compile in thumb by default (newlib is also compiled in thumb)
- Fixed fs calls. Vita newlib has a not-very-posix dirent. Also vita does not expose inodes, it's stubbed as 0 in stat, and I'm stubbing it here for dirent (because vita newlibs's dirent doesn't even have that field)
- Enabled signal handlers for panic unwinding
- Dropped static link requirement from the platform support md. Also, rearranged sections to better stick with the template.

Author: bors