Disable -Xlinker argument reordering test on macOS.

[spevans]

Fixes broken test introduced by #9958

The linker argument reordering test should only be run on Linux.

[CodaFi]

Thanks for getting to this so quickly.

@swift-ci please smoke test

[spevans]

/cc @jrose-apple Last PR introduced a bad test, should probably do a full test to check its ok

[jrose-apple]

Whoops, my bad, thanks. It might be better here to not use %target-swiftc_driver and instead just pass an explicit -target to %swiftc_driver.

[jrose-apple]

(but we can get this in first to unbreak the bots)

[spevans]

-target would still be problematic on macOS due to some of the linux files not being present (maybe something to fix for the cross compiling at some point)

/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2017-07-13-a.xctoolchain/usr/bin/swiftc -target x864_64-linux-gnu -driver-print-jobs -static-stdlib -o /tmp/test1 -Xlinker --no-allow-multiple-definition /tmp/test.swift 
LLVM ERROR: /Users/spse/Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2017-07-13-a.xctoolchain/usr/lib/swift_static/linux/static-stdlib-args.lnk not found