attempt to fix autoconf ObjC runtime check
attempt to fix autoconf ObjC runtime check

Signed-off-by: Daniel A. Steffen <bebabb62faccb84a5df481779a4e9f0603fce05c@apple.com>

apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch,apple/swift-corelibs-libdispatch