Workaround build error for mingw-g++

mingw-g++ does not correctly support the full `std::errc` namespace as
worded in the standard[1]. As such, we cannot reliably use all names
therein. This patch changes the use of
`std::errc::state_not_recoverable`, to use portable error codes from the
`llvm::errc` equivalent.

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71444

Reviewed by v.g.vassilev
Differential Revision: https://reviews.llvm.org/D111315