includes: move tb_flush into its own header

This aids subsystems (like gdbstub) that want to trigger a flush
without pulling target specific headers.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

Message-Id: <20230302190846.2593720-8-alex.bennee@linaro.org>
Message-Id: <20230303025805.625589-8-richard.henderson@linaro.org>

linux-user/user-internals.h

@@ -20,6 +20,7 @@
 
 #include "exec/user/thunk.h"
 #include "exec/exec-all.h"
+#include "exec/tb-flush.h"
 #include "qemu/log.h"
 
 extern char *exec_path;