On AIX, this test generates an XCOFF file and hits "unknown binary format" assertion in llvm-nm. This patch specifies the triple to mitigate this issue.
Change looks okay. Specifically: The test is for bitcode embedded in Mach-O, so the change made probably doesn't affect the primary purpose of the test (since the Mach-O aspect was encoded in the first RUN line). In other words, adding the triple is not removing significant coverage for other targets.
Aside: I think the default_triple requirement can be removed?