Protect DWARFCompileUnit::m_die_array by new mutexes

If BuildAddressRangeTable called ExtractDIEsIfNeeded(false), then another
thread started processing data from m_die_array and then the first thread
called final ClearDIEs() the second thread would crash.

It is also required without multithreaded debugger using DW_TAG_partial_unit
for DWZ.

Differential revision: https://reviews.llvm.org/D40470

llvm-svn: 333987