Adding an explicit pgma flag for interaction with GHC

[zlonast]

Add an explicit pgma flag to Cabal's GHC invocation logic. Pass the assembler
program explicitly to GHC. This change allows users to specify a custom as
program to compile assembly manually.

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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[zlonast]

Apparently if I pass gcc instead of as I get a bunch of warnings, I think it's a ghc bug.

https://gitlab.haskell.org/ghc/ghc/-/issues/27216

[127 of 148] Compiling Distribution.Simple.GHC ( ... ) [Source file changed]
clang: warning: argument unused during compilation: '-fno-common' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-U PIC' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-D PIC' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-fno-common' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-U PIC' [-Wunused-command-line-argument]
clang: warning: argument unused during compilation: '-D PIC' [-Wunused-command-line-argument]

[1 of 1] Compiling Main ( ... ) [Missing object file]
nasm: fatal: unrecognised output format no-common' - use -hf for a list Usage: nasm [-@ response_file] [options...] [--] filename For additional help: nasm -h [run|topics|all|-option] <no location info>: error: as-wrapper.sh' failed in phase `Assembler'. (Exit code: 1)