pretty_printer: rename instances named "buffer" to "pp"

pretty_printer: rename instances named "buffer" to "pp"

Various pretty_printer instances are named "buffer", but a
pretty_printer *has* a buffer, rather than *is* a buffer.

For example,

  pp_buffer (buffer)->digit_buffer

is referring to "buffer"'s buffer's digit_buffer.

This mechanical patch renames such variables to "pp", which I find much
clearer; the above becomes:

  pp_buffer (pp)->digit_buffer

i.e. "pp's buffer's digit_buffer".

No functional change intended.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>
gcc/c-family/ChangeLog:
	* c-ada-spec.cc: Rename pretty_printer "buffer" to "pp"
	throughout.

gcc/ChangeLog:
	* gimple-pretty-print.cc: Rename pretty_printer "buffer" to "pp"
	throughout.
	* print-tree.cc (print_node): Likewise.
	* tree-loop-distribution.cc (dot_rdg_1): Likewise.
	* tree-pretty-print.h (dump_location): Likewise.
	* value-range.cc (vrange::dump): Likewise.
	(irange_bitmask::dump): Likewise.

Signed-off-by: David Malcolm <dmalcolm@redhat.com>