[Object, MachO] Mark symbols from DATA and BSS sections as ST_Data

In `MachOObjectFile::getSymbolType` we currently always return `SymbolRef::ST_Function` for symbols from any section. In order for llvm-symbolizer to correctly symbolize Mach-O globals, symbols from data and BSS sections should return `SymbolRef::ST_Data`.

Differential Revision: http://reviews.llvm.org/D14576

llvm-svn: 252867