[llvm-objdump] properly use c_str() with format("%s").  Improve getLibraryShortNameByIndex() error handling.





git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217930 91177308-0d34-0410-b5e6-96231b3b80d8
Fix identify_magic() with mach-o stub dylibs.

The wrong value was returned and the unittest did not cover the stub dylib case.




git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217933 91177308-0d34-0410-b5e6-96231b3b80d8