cmake PG should ensure correct libdir, otherwise ports are broken on linux

[Fred Wright]

On Tue, 17 Sep 2024, Ken Cunningham wrote:

> Linux surely looks in lib64. MacPorts might not be configuring linux to 
> look in lib64 though.

"Linux", in the sense of its dynamic linker, doesn't directly "look in 
directories" at all.  It uses the cache of locations of specific libraries 
created by ldconfig, by *its* scan of the directories.  There's a config 
file telling ldconfig which directories to scan, which is most likely 
correctly set up to include all the "usual suspects".  But it doesn't do 
any good if you don't rerun ldconfig after adding libraries.

Fred Wright