comp-v2-builder: pass --with-PROG directly for cabal's built-in programs
cabal's `Distribution.Simple.Program.Db.userSpecifyPath` silently
ignores `--with-PROG=PATH` for any program not pre-registered in the
`ProgramDb` (the underlying `Map.update` over `unconfiguredProgs`
is a no-op for unknown names). The 24 built-in programs from
`Distribution.Simple.Program.Builtin.builtinPrograms` (alex, happy,
c2hs, hsc2hs, cpphs, hscolour, doctest, haddock, etc.) are
pre-registered, so cabal v2-build accepts `--with-NAME=PATH` for them
directly. Arbitrary build-tool-exes (e.g. `pkga-exe`) aren't —
cabal v2-build rejects those with "unrecognized 'v2-build' option".
The previous `--configure-option=--with-NAME=PATH` blanket-wrap
worked for arbitrary names but broke the built-in case: wrapping
threads the flag through to per-package Setup configure, which DOES
register the override in its own ProgramDb, but cabal v2-build's
OWN program resolution (used for the per-slice preprocess invocations
like "Running alex…") never sees the override and falls back to the
cross-target binary in the bundled cabal-store. Concretely:
language-c's alex preprocess step ran the cross-target aarch64 alex
on an x86_64 build host, producing "posix_spawnp: invalid argument
(Exec format error)".
Split the flag emission accordingly:
* built-in: emit `--with-NAME=PATH` directly to `cabal v2-build`
* non-built-in: emit `--configure-option=--with-NAME=PATH`
Verified by `tests.th-dlls.build` on
`ghc9141llvm.aarch64-multiplatform` (previously failed on
language-c's alex invocation, now builds through to th-dlls).
