Re: [PoC] Federated Authn/z with OAUTHBEARER

Hello!

This patch fixes CPPFLAGS, LDFLAGS, LIBS when checking AsyncDNS libcurl
support in configure

Custom parameters and paths to libcurl were mistakenly excluded from
CPPFLAGS, LDFLAGS, and LIBS, although AsyncDNS check was OK.

For example, the command `pkg-config --libs libcurl` gives
`-L/usr/local/lib -lcurl`. LDFLAGS will not contain `-L/usr/local/lib`.

This patch fixes such behaviour.

Test case:

I've tested custom Postgres in an old Debian based Linux distro. This
distro contains old libcurl (< 7.61, package libcurl3) that was compiled
with symbols CURL_OPENSSL_3. So I've installed newer version of
libcurlssl, package libcurl4-openssl-dev, that contains symbols
CURL_OPENSSL_4 and compiled my libcurl version > 7.61.

After compilation during testing some Postgres shared libraries or
binaries that was linked with libcurl showed an error "version
CURL_OPENSSL_3 not found (required by …/libcurl.so.4)"

--
Best wishes,
Ivan Kush
Tantor Labs LLC