diagnostics/libcpp: convert enum location_aspect to enum class

diagnostics/libcpp: convert enum location_aspect to enum class

Modernization; no functional change intended.

gcc/ChangeLog:
	* diagnostics/paths-output.cc: Update for conversion of
	location_aspect to enum class.
	* diagnostics/source-printing.cc: Likewise.
	* input.cc: Likewise.
	* input.h: Likewise.

libcpp/ChangeLog:
	* include/line-map.h (enum location_aspect): Convert to...
	(enum class location_aspect): ...this.
	* line-map.cc: Update for conversion of location_aspect to enum
	class.

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