Fix the interpretation of a 0 st_name.

Fix the interpretation of a 0 st_name.

The ELF spec is very clear:

-----------------------------------------------------------------------------
If the value is non-zero, it represents a string table index that gives the
symbol name. Otherwise, the symbol table entry has no name.
--------------------------------------------------------------------------

In particular, a st_name of 0 most certainly doesn't mean that the symbol has
the same name as the section.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238899 91177308-0d34-0410-b5e6-96231b3b80d8