Completed conversion of TSourceLoc into a struct

TSourceLoc was defined as an int, but is meant to be
used as a struct to carry all the information provided
by the parser, so the conversion was made in this cl.

Change-Id: I6015d11aafda96914ec7b2c37883ffbc963a08fe
Reviewed-on: https://swiftshader-review.googlesource.com/3664
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>