Minor BRIG/HSAIL frontend updates and bug fixes:

Minor BRIG/HSAIL frontend updates and bug fixes:

* brig-builtins.def: Added a builtin for class_f64.
* builtin-types.def: Added a builtin type needed by class_f64.
* brigfrontend/brig-code-entry-handler.cc
 (brig_code_entry_handler::build_address_operand): Fix a bug
 with reg+offset addressing on 32b segments. In large mode,
 the offset is treated as 32bits unless it's global, readonly or
 kernarg address space.
* rt/workitems.c: Removed a leftover comment.
* rt/arithmetic.c (__hsail_class_f32, __hsail_class_f64): Fix the
 check for signaling/non-signalling NaN. Add class_f64 default
 implementation.

From-SVN: r247576