on armv4 that doesn't support this instruction. Futhermore pld is a nop on some
armv5 processor like arm926. Detect if pld is supported and have the
preprocessor remove it when it's not supported.
Fixes issue 393.
patch by matthieu castet, castet.matthieu free fr


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@12569 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b