[fir] Add complex operations conversion from FIR LLVM IR

This patch add conversion for primitive operations on complex types.
- fir.addc
- fir.subc
- fir.mulc
- fir.divc
- fir.negc

This adds also the type conversion for !fir.complex<KIND> type.

This patch is part of the upstreaming effort from fir-dev branch.

This patch was updated to avoid failure on windows buildbot.
Flang codegen does not support windows target so we force the test
to use a known target instead.

Reviewed By: kiranchandramohan, rovka

Differential Revision: https://reviews.llvm.org/D113434



Co-authored-by: Jean Perier <jperier@nvidia.com>
Co-authored-by: Eric Schweitz <eschweitz@nvidia.com>