MFH: r551634 r551663 r551702 r552356

databases/postgresql13-server: fix build on GCC architectures

Add the previously removed disabling of LLVM when it's not in base.

databases/postgresql13-server: fix build on clang architectures

Move LLVM option configuration after including bsd.port.options.mk.

Reported by: kib@

databases/postgresql13-server: make LLVM option unselectable

This will still keep this port and its slaves buildable on the package builder on powerpc64, and I doubt anyone uses it on mips*.

Reported by: kib@, adamw@

Fix options breakage from r551702.

Make LLVM option work again on everything but powerpc64.

PR: 250346
Submitted by: Christian Ullrich

Approved by: portmgr (fix build blanket)