SERVER-14835 - fix fassert 16143 on PPC64 LE systems in LogFile::synchronousAppend()

new version, using ioctl(_fd, BLKBSZGET) and fixed predefined alignment for PPC64.
Unfortunately, AlignedBuilder::Alignment being static const, we'd need to either make it runtime changeable (bad) or use a macro. We can also use one defined by scons and filled with the result of $(getconf PAGESIZE) on Linux systems.