Since Xcode 15 beta 6, ld -v output differs from previous versions:
* macOS 13/Xcode 14:
@(#)PROGRAM:ld PROJECT:ld64-857.1
* macOS 14/Xcode 15:
@(#)PROGRAM:ld PROJECT:dyld-1015.1
configure cannot handle the new form, so LD64_VERSION isn't set.
This patch fixes this. The autoconf manual states that sed doesn't
portably support alternation, so I'm using two separate expressions to
extract the version number.