databases/postgresql92-server: set LLD_UNSAFE

postgresql*-client ports fail to build with lld as /usr/bin/ld with
errors like

/usr/bin/ld: error: can't create dynamic relocation R_X86_64_PC32 against

symbol: __mb_sb_limit in readonly segment

defined in /lib/libc.so.7
referenced by pgstrcasecmp.c

pgstrcasecmp.o:(pg_strcasecmp) in archive

../../src/port/libpgport.a

Although this appears to affect only -client ports, just set LLD_UNSAFE
for all of the postgresql*-* ports for simplicity.

Approved by: portmgr (blanket for LLD_UNSAFE)