[llvm-nm] add a new option -X to specify the type of object file llvm-nm should examine

Summary:
Added a new option "-X" to specify, which type of object file should be examine.

For example:

1. "llvm-nm -X64 archive.a" only deal with the 64bit object files in the archive.a ,ignore the all 32bit object files in the archive.a
2. "llvm-nm -X32 xcoffobj32.o xcoffobj64.o " only deal with the 32bit object file "xcoffobj32.o" , 64bit object file "xcoffobj64.o" will be ignored

Reviewers: James Henderson,Fangrui Song
Differential Revision: https://reviews.llvm.org/D118193