[ORC] Track JIT symbol states more explicitly.

Prior to this patch, JITDylibs inferred symbol states (whether a symbol was
newly added, materializing, resolved, or ready to run) via a combination of (1)
bits in the JITSymbolFlags member, and (2) the state of some internal JITDylib
data structures. This patch explicitly tracks symbol states by adding a new
SymbolState member to the symbol table entries, and removing the 'Lazy' and
'Materializing' bits from JITSymbolFlags. This is a first step towards adding
additional states representing initialization phases (e.g. eh-frame registration,
registration with the language runtime, and static initialization).

llvm-svn: 361899