config.mak.uname: avoid macOS linker warning on Xcode 16.3+

config.mak.uname: avoid macOS linker warning on Xcode 16.3+

Building on macOS with Xcode 16.3 or newer emits:

    ld: warning: reducing alignment of section __DATA,__common
    from 0x8000 to 0x4000 because it exceeds segment maximum
    alignment

Pass -fno-common when "ld -v" reports ld-1167 or newer, so tentative
definitions of large arrays go into BSS instead of __DATA,__common.

Signed-off-by: Harald Nordgren <haraldnordgren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>