The syscall package now defines [WSAENOPROTOOPT] on Windows....

When preparing any change that is permitted by Go 1 compatibility
but may nonetheless break some existing programs,
we first engineer the change to keep as many existing programs working as possible.
For the remaining programs,
we define a new GODEBUG setting that
allows individual programs to opt back in to the old behavior.
A GODEBUG setting may not be added if doing so is infeasible,
but that should be extremely rare.

Its type must be a <a href="#Type_definitions">defined</a> type <code>T</code> or a
pointer to a defined type <code>T</code>, possibly followed by a list of type parameter
names <code>[P1, P2, …]</code> enclosed in square brackets.
<code>T</code> is called the receiver <i>base type</i>. A receiver base type cannot be
a pointer or interface type and it must be defined in the same package as the method.

The `debug/elf` package now defines [PT_OPENBSD_NOBTCFI]. This [ProgType] is
used to disable Branch Tracking Control Flow Integrity (BTCFI) enforcement