Introduce gdb.interrupt

DAP cancellation needs a way to interrupt whatever is happening on
gdb's main thread -- whether that is the inferior, a gdb CLI command,
or Python code.

This patch adds a new gdb.interrupt() function for this purpose.  It
simply sets the quit flag and lets gdb do the rest.

No tests in this patch -- instead this is tested via the DAP
cancellation tests.

Reviewed-By: Eli Zaretskii <eliz@gnu.org>
Reviewed-By: Kévin Le Gouguec <legouguec@adacore.com>
3 files changed