gdbstub: move chunks of user code into own files

The process was pretty similar to the softmmu move except we take the
time to split stuff between user.c and user-target.c to avoid as much
target specific compilation as possible. We also start to make use of
our shiny new header scheme so the user-only helpers can be included
without the rest of the exec/gsbstub.h cruft.

As before we split some functions into user and softmmu versions

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20230302190846.2593720-12-alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-12-richard.henderson@linaro.org>

include/gdbstub/user.h

@@ -0,0 +1,43 @@
+/*
+ * gdbstub user-mode only APIs
+ *
+ * Copyright (c) 2022 Linaro Ltd
+ *
+ * SPDX-License-Identifier: LGPL-2.0+
+ */
+
+#ifndef GDBSTUB_USER_H
+#define GDBSTUB_USER_H
+
+/**
+ * gdb_handlesig() - yield control to gdb
+ * @cpu: CPU
+ * @sig: if non-zero, the signal number which caused us to stop
+ *
+ * This function yields control to gdb, when a user-mode-only target
+ * needs to stop execution. If @sig is non-zero, then we will send a
+ * stop packet to tell gdb that we have stopped because of this signal.
+ *
+ * This function will block (handling protocol requests from gdb)
+ * until gdb tells us to continue target execution. When it does
+ * return, the return value is a signal to deliver to the target,
+ * or 0 if no signal should be delivered, ie the signal that caused
+ * us to stop should be ignored.
+ */
+int gdb_handlesig(CPUState *, int);
+
+/**
+ * gdb_signalled() - inform remote gdb of sig exit
+ * @as: current CPUArchState
+ * @sig: signal number
+ */
+void gdb_signalled(CPUArchState *as, int sig);
+
+/**
+ * gdbserver_fork() - disable gdb stub for child processes.
+ * @cs: CPU
+ */
+void gdbserver_fork(CPUState *cs);
+
+
+#endif /* GDBSTUB_USER_H */