[xmlsec] Fix to configure when OpenSSL is in /usr/lib

[Scott Cantor]

I'd like to suggest a change to the autoconf script so that when OpenSSL
is in a default system location like /usr/lib, the script doesn't embed
/usr/lib and /usr/include in the compiler/linker flags.

The reason I see this as a problem is that for, say Linux, where OpenSSL
tends to be installed there, if I want to build xmlsec using newer
versions of libxml2 and libxslt then are installed as rpms, I'd like to
be able to do that in a custom location and have xmlsec find them
instead of the default versions.

Many people are reluctant or unwilling to update libxml2 and friends
until Red Hat blesses them, since GNOME is sitting on top of them, and
RH 8.0 does not ship with up to date versions that will let xmlsec link.

I have a crude patch I could suggest for this, but would be happy to
defer to you or others that might want to do this a specific way.

-- Scott