Adding an explicit pgmcxx flag for interaction with GHC

[zlonast]

Add an explicit pgmcxx flag to Cabal's GHC invocation logic. This aligns
with the existing pgmc behavior and accounts for the GHC 9.4+ toolchain
requirements, resolving inconsistencies in how C++ compiler options are handled.

This change allows users to remove extra-libraries: stdc++ from their
configuration files, as g++ automatically handles C++ standard library
linking, unlike the legacy approach of invoking C++ via gcc.

Main idea #9801 (comment)

IMHO, cc-options (and ld-options and cpp-options and ...) should be always passed when invoking GHC, similarly as ghc-options should be always used when invoking ghc - regardless of what is the intention of a particular GHC-call. GHC might use or not use the options, Cabal cannot know and should not guess.

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