[AIX] change "llvm-nm" to "env OBJECT_MODE=any llvm-nm" in clang/test for AIX OS

Summary:
   since default object mode of llvm-nm is change to -X32 (from default -Xany) in patch https://reviews.llvm.org/D132494.In order not effect the test cases in clang/test we need to change "llvm-nm" to "env OBJECT_MODE=any llvm-nm" in clang/test for AIX OS

Reviewers: James Henderson,David Tenty, Hubert Tong
Differential Revision: https://reviews.llvm.org/D134284