binutils: build host version statically

Otherwise we end up with libbfd/libopcodes in host/usr/$BUILD/$TARGET/lib,
used by the binaries. Unfortunately it also adds rpaths, which first look
in the build directory before here, causing trouble if the toolchain is
used outside BR (E.G. for a SDK) and the build directory location reused
for another incompatible build (E.G. another ARCH), as the binutils
binaries then end up using the wrong libs.

Fix it by linking statically instead.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>