Add LOCALBASE-based ldconfig dir to plist for non-default PREFIX

ldconfig file is always installed into LOCALBASE-based directory
(${LOCALBASE}/${LDCONFIG_DIR}) which is first created. When a port
redefines PREFIX (PREFIX != LOCALBASE), this directory needs to be
mentioned in pkg-plist.

Add the directory to the plist. While here, add identation to nested
make conditions and loops to improve readability and simplify one
empty .if body.

This fixes stage-qa for biology/emboss and cad/brlcad

Approved by: portmgr (bapt)
Differential Revision: D3815