It appears that LIB/LINK default to the host architecture if they can't
guess it from the first object. With the MSVC toolchain, resource files
are (usually) compiled to an arch-neutral .res format. Always
explicitly provide a '/MACHINE:' argument to avoid it guessing
incorrectly when cross-compiling.
ninja chokes when building FFmpeg's static libraries, as the
command line can be larger than 32000.
This was disabled on purpose in #1649, but the rsp syntax was
different: this commit makes it so the options and output file
are still passed on the command line, gcc-ar didn't work
otherwise.