clover: Allow build with -Dcpp_rtti=false on Windows
Fixes: ad862674 ("meson: Don't override built-in cpp_rtti option, error if it's invalid")
!13064 (merged) allowed RTTI mismatch when building clover with MSVC but failed to allow -Dcpp_rtti=false
for MSVC.
There was an opportunity to correct this in !17055 (merged) but it was missed.
Edited by Prodea Alexandru-Liviu