init alpine 13.1 gcc

this drops:

• everything with an empty cherry-pick
• 2 go patches (syscall, runtime: always call XSI strerror_r, libgo: permit loff_t and off_t to be macros) that are nonempty but fixed otherwise
• 2 mips patches (we dropped the architecture)

this is based directly on Apr 29 daily bump, not 13.1 release- there are more fixes in the branch after the tag, and we follow the branch anyway

wip, still have to test if it builds, etc