* [lit] Port Support %if ... %else syntax for RUN lines from upstream
Based on
1041a9642b
This syntax allows to modify RUN lines based on features
available. For example:
RUN: ... | FileCheck %s --check-prefix=%if windows %{CHECK-W%} %else %{CHECK-NON-W%}
CHECK-W: ...
CHECK-NON-W: ...
This is merged to allow dxilver check apply on each RUN line.