sim/rx/gdb-if.c had a function named `rx_signal_to_host'. This
function mapped signal numbers used by the BSP to host signal
numbers which, at one time a while back, were used by GDB
as target signal numbers. This change updates the signal
numbers returned to be those names prefixed with "GDB_SIGNAL_"
as defined in include/gdb/signals.h.
It also changes the name of the function somewhat to better
match what the function currently does. I noticed that this
function is not static - and there's no reason for it not
to be - so I made it static too.
* gdb-if.c (rx_signal_to_host): Rename to
`rx_signal_to_gdb_signal'. Make static. Update all callers
to use new name. Use signal names from include/gdb/signals.h.