Revision 522745

audio/ardour5: fix build on powerpc64

_POSIX_SOURCE causes some errors in errno.h not to be seen (like EAFNOSUPPORT), so remove it.

On ELFv2 lld can't link it, throws errors like:
ld: error: relocation R_PPC64_ADDR32 cannot be used against local symbol; recompile with -fPIC
>>> defined in libs/ardour/cycle_timer.cc.1.o
>>> referenced by cycle_timer.cc
>>>               libs/ardour/cycle_timer.cc.1.o:(__ftr_fixup+0x8)

Recompiling with -fPIC doesn't help, so use GNU ld there.

PR:		243281
Approved by:	portmgr (blanket: build fix)
MFH:		2020Q1 (blanket: build fix)