Use pkg-config for configuring LDFLAGS

[peterstace]

Description

This is to allow the github.com/peterstace/geos package to compile on new M2 Macs.

Check List

Have you:

• Added unit tests? N/A

• Add cmprefimpl tests? (if appropriate?) N/A

• Updated release notes? (if appropriate?) N/A

Related Issue

• N/A

[peterstace]

Thanks for reviewing @albertteoh ! 😁