cmake: allow pkg-config in more envs

[vszakats]

Before this patch, pkg-config was used for UNIX builds only (with
a few exceptions like wolfSSL, libssh, gsasl, libuv). This patch extends
pkg-config use to all envs except: MSVC without vcpkg. Meaning MSVC
with vcpkg will now use it. Also mingw on Windows.

Also apply the new condition to options where pkg-config was used
unconditionally (= for all targets). These are:
-DCURL_USE_WOLFSSL=ON, -DCURL_USE_LIBSSH=ON,
-DCURL_USE_GSASL=ON and -DCURL_USE_LIBUV=ON

This patch may still cause regressions for cross-builds (e.g. mingw
cross-build from Unix) and potentially other cases. If that happens, we
recommend using some of these methods to explicitly disable pkg-config
when using CMake:

• CMake option: -DPKG_CONFIG_EXECUTABLE=
  (or -DPKG_CONFIG_EXECUTABLE=nonexistent or similar)
  This is similar to the (curl-specific) PKG_CONFIG env for autotools.
• export env: PKG_CONFIG_LIBDIR=
  (or PKG_CONFIG_PATH, PKG_CONFIG_SYSROOT_DIR,
  or the CMake-specific PKG_CONFIG)

We may improve control over this in a future patch, also allowing opting
in MSVC (without vcpkg).

Ref: #14405
Ref: #14408
Ref: #14140
Closes #14483

---

• apply to all other case where if(UNIX) is used.
• apply to CURL_USE_WOLFSSL, CURL_USE_LIBSSH, CURL_USE_GSASL, CURL_USE_LIBUV.
• replace this condition with an overridable CURL_USE_PKGCONFIG setting. → cmake: add CURL_USE_PKGCONFIG option #14504
• add initial pkg-config support for deps which don't have it yet.

Without whitespace: https://github.com/curl/curl/pull/14483/files?w=1

[talregev]

Why not msvc?

[vszakats]

It is MSVC, but only when combined with vcpkg. In other MSVC cases, pkg-config is reported to break builds: #14405 #14365. Also outside vcpkg, pkg-config means mingw-specific options and libs.

Or, is there any raw/other MSVC env out there that supports pkg-config?

[talregev]

Or, is there any raw/other MSVC env out there that supports pkg-config?

I don't familiar with more.
Thank you for the detailed answer.