Make sure we don't crash if someone (E.G.) comments out on entry from g_core_definitions[] without removing the ArchSpec::Core enumeration when submitting from source.

We now catch the issue with a static_assert() at compile time and use llvm::array_lengthof(g_core_definitions) as well.

<rdar://problem/17767541>



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@213778 91177308-0d34-0410-b5e6-96231b3b80d8