This fixes generating shared libraries with a toolchain that requires
makedef (MSVC, or mingw toolchains with LLD, that lacks support for
--version-script).
This uses the existing response file generated for linking, by
splitting out the choice of input parameter to makedef to a variable
expanded by make.
This avoids relying on "echo" within makedef supporting long command
lines; msys2/cygwin shells handle it fine, while busybox doesn't.
Martin Storsjö
8512161c81