Make loop counter unsigned in SymbolFilePDB::GetCompileUnitIndex

[teemperor]

Summary

This fixes a clang warning.

[zturner]

Trivial fixes like this don't need to be reviewed, you can just commit them. Thanks for your work btw!

lldb/trunk/source/Plugins/SymbolFile/PDB/SymbolFilePDB.cpp

void SymbolFilePDB::GetCompileUnitIndex(
     uint32_t &index) {
   if (!pdb_compiland)
     return;
 
   auto results_up = m_global_scope_up->findAllChildren<PDBSymbolCompiland>();
   if (!results_up)
     return;
   auto uid = pdb_compiland->getSymIndexId();
-  for (int cu_idx = 0; cu_idx < GetNumCompileUnits(); ++cu_idx) {
+  for (uint32_t cu_idx = 0; cu_idx < GetNumCompileUnits(); ++cu_idx) {
     auto compiland_up = results_up->getChildAtIndex(cu_idx);
     if (!compiland_up)
       continue;
     if (compiland_up->getSymIndexId() == uid) {
       index = cu_idx;
       return;
     }
   }