gdbstub: Introduce gdb_handle_query_supported_user()

The upcoming follow-fork-mode child support requires advertising the
fork-events feature, which is user-specific. Introduce a user-specific
hook for this.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Message-Id: <20240219141628.246823-9-iii@linux.ibm.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240305121005.3528075-10-alex.bennee@linaro.org>
diff --git a/gdbstub/user.c b/gdbstub/user.c
index 866a25f..c9e8b83 100644
--- a/gdbstub/user.c
+++ b/gdbstub/user.c
@@ -382,6 +382,10 @@
     disable_gdbstub(cpu);
 }
 
+void gdb_handle_query_supported_user(const char *gdb_supported)
+{
+}
+
 /*
  * Execution state helpers
  */