Re: typedefs.list glitches

I wrote:
> every buildfarm member that's contributing to the typedefs list
> builds with OpenSSL.  That wouldn't surprise me, except that
> my own animal sifaka should be filling that gap.  Looking at
> its latest attempt[1], it seems to be generating an empty list,
> which I guess means that our recipe for extracting typedefs
> doesn't work on macOS/arm64.  I shall investigate.

Found it.  Current macOS produces

$ objdump -W
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/objdump: error: unknown argument '-W'

where last year's vintage produced

$ objdump -W
objdump: Unknown command line argument '-W'.  Try: '/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/objdump --help'
objdump: Did you mean '-C'?

This confuses run_build.pl into taking the "Linux and sometimes windows"
code path instead of the $using_osx one.  I think simplest fix is to
move the $using_osx branch ahead of the heuristic ones, as attached.

			regards, tom lane