FindPkgConfig: Restore finding pkg-config before pkgconf

Since commit 94a84dc0 (FindPkgConfig: add pkgconf to the search list.,
2021-07-02, v3.22.0-rc1~468^2), `pkgconf` is preferred over `pkg-config`
if they appear in the same directory.  In some environments,
`pkg-config` may be a wrapper that adds semantics beyond either
`pkgconf` or the normal `pkg-config`.  Prefer `pkg-config` over
`pkgconf` in order to preserve the prior behavior in such environments.

Fixes: #22976
30 jobs for !6780 with FindPkgConfig-pkgconf in 17 minutes and 42 seconds (queued for 1 second)
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