[lld-macho][test] Rename dtrace test (NFC)

This matches the convention used elsewhere

Differential Revision: https://reviews.llvm.org/D131456

diff --git a/lld/test/MachO/x86_64-dtrace.s b/lld/test/MachO/x86-64-dtrace.s
similarity index 100%
rename from lld/test/MachO/x86_64-dtrace.s
rename to lld/test/MachO/x86-64-dtrace.s