libbacktrace / mingw-w64 / fPIC ignored for target (all code is position independent)

[Christer Solskogen]

I get this when I'm building a cross compiler for mingw-w64
with gcc-trunk now:
libbacktrace/unknown.c:1:0: error: -fPIC ignored for target 
(all code is position 
independent) [-Werror]

using --disable-werror does not fix it. 
The workaround I found was to remove -fPIC from PIC_FLAG in 
$builddir/x86_64-w64-mingw32/libbacktrace/Makefile.