plugins/api: split out binary path/start/end/entry code

To move the main api.c to a single build compilation object we need to
start splitting out user and system specific code. As we need to grob
around host headers we move these particular helpers into the *-user
mode directories.

The binary/start/end/entry helpers are all NOPs for system mode.

While using the plugin-api.c.inc trick means we build for both
linux-user and bsd-user the BSD user-mode command line is still
missing -plugin. This can be enabled once we have reliable check-tcg
tests working for the BSDs.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20250304222439.2035603-27-alex.bennee@linaro.org>

plugins/api-system.c

@@ -0,0 +1,39 @@
+/*
+ * QEMU Plugin API - System specific implementations
+ *
+ * This provides the APIs that have a specific system implementation
+ * or are only relevant to system-mode.
+ *
+ * Copyright (C) 2017, Emilio G. Cota <cota@braap.org>
+ * Copyright (C) 2019-2025, Linaro
+ *
+ * SPDX-License-Identifier: GPL-2.0-or-later
+ */
+
+#include "qemu/osdep.h"
+#include "qemu/main-loop.h"
+#include "qemu/plugin.h"
+
+/*
+ * In system mode we cannot trace the binary being executed so the
+ * helpers all return NULL/0.
+ */
+const char *qemu_plugin_path_to_binary(void)
+{
+    return NULL;
+}
+
+uint64_t qemu_plugin_start_code(void)
+{
+    return 0;
+}
+
+uint64_t qemu_plugin_end_code(void)
+{
+    return 0;
+}
+
+uint64_t qemu_plugin_entry_code(void)
+{
+    return 0;
+}