OpenBSD 5.9 apparently defaults to -fpie. We use -fno-PIE when appropriate
already, but that is not enough - it does not turn off -fpie.

Actually check for -fPIE is not precise enough. __PIE__ is set for both
-fpie and -fPIE but with different values. As far as I can tell, both
options were introduced at the same time, so both should always be supported.

This fixes compilation on OpenBSD 5.9 which otherwise created insanely big
lzma_decompress.img.

Reported, suggested and tested by: Jiri B <jirib@devio.us>