Rename location accessor macro parameters to silence ARI

Rename location accessor macro parameters to silence ARI

The locations patch I recently committed contains macro definitions
such as:

This causes an ARI error to be emitted by the server ("Do not use PTR, ISO C
90 implies `void *'").  While this ARI error is bogus in this context,
it is just easiest to squash the error completely by renaming the macro
parameters.

gdb/ChangeLog

	* location.c (EL_TYPE, EL_LINESPEC, EL_PROBE, EL_ADDRESS)
	(EL_EXPLICIT, EL_STRING): Change macro parameter to "P" to
	silence ARI errors.