rpc: genprotocol: Always apply fixups to rpcgen's output

rpc: genprotocol: Always apply fixups to rpcgen's output

The platform check which determines when to apply the fixups mentions
all officially supported build targets (per docs/platforms.rst) thus
it's not really necessary.

Additionally while not explicitly written as supported the check does
not work properly when building with the MinGW toolchain on Windows as
it does not apply the needed transformations. They are necessary
there the same way as with MinGW on Linux.

https://gitlab.com/libvirt/libvirt/-/issues/453

Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>