Cabal should respect PKG_CONFIG

[wenkokke]

Describe the bug Cabal should probably respect the PKG_CONFIG environment variable, rather than hard-coding the name "pkg-config", as done in, e.g., Distribution.Simple.Program.Builtin. For instance, mingw packages are moving to use pkgconf, which leads to trouble with Cabal, as pkg-config and pkgconf cannot both be installed.

[mouse07410]

If memory serves me, PKG_CONFIG env var is used by other package managers, besides Cabal. Thus, relying on it here could be problematic.

[gbaz]

Is that env var documented as a standard anywhere or is it just widespread convention?

[mouse07410]

I can't recall. Sorry!

[arrowd]

FreeBSD also uses pkgconf but we also install the pkg-config symlink pointing to pkgconf. Maybe MinGW should do the same?

If an utility is intended to be a drop-in replacement and not intended to be coinstalled, I'd rather fix it on the packaging side.