Support parsing defined operator generated by macro expansion

Support parsing defined operator generated by macro expansion

dEQP tests enforce that the defined operator should be parsed even when
it is generated as a result of macro expansion, even though this is
undefined according to the C++ preprocessor spec.

Implement support for this by putting the parsing for the defined
operator inside MacroExpander. The operator gets processed right after
it is generated by macro expansion. Parsing the defined operator is
toggled with a boolean according to the context where MacroExpander
is used.

Change-Id: I8557e829f4278ab6cb27eb4a0f84ca0c0dd18d1a
Reviewed-on: https://swiftshader-review.googlesource.com/5182
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>