Update LLVM for rebase to r212749.

Includes a cherry-pick of:
r212948 - fixes a small issue with atomic calls

Change-Id: Ib97bd980b59f18142a69506400911a6009d9df18
diff --git a/lib/DebugInfo/DWARFUnit.cpp b/lib/DebugInfo/DWARFUnit.cpp
index f5f5072..39d0a0f 100644
--- a/lib/DebugInfo/DWARFUnit.cpp
+++ b/lib/DebugInfo/DWARFUnit.cpp
@@ -226,7 +226,9 @@
     AddrOffsetSectionBase = DieArray[0].getAttributeValueAsSectionOffset(
         this, DW_AT_GNU_addr_base, 0);
     RangeSectionBase = DieArray[0].getAttributeValueAsSectionOffset(
-        this, DW_AT_GNU_ranges_base, 0);
+        this, DW_AT_ranges_base, 0);
+    // Don't fall back to DW_AT_GNU_ranges_base: it should be ignored for
+    // skeleton CU DIE, so that DWARF users not aware of it are not broken.
   }
 
   setDIERelations();
@@ -272,7 +274,8 @@
   }
   // Share .debug_addr and .debug_ranges section with compile unit in .dwo
   DWOCU->setAddrOffsetSection(AddrOffsetSection, AddrOffsetSectionBase);
-  DWOCU->setRangesSection(RangeSection, RangeSectionBase);
+  uint32_t DWORangesBase = DieArray[0].getRangesBaseAttribute(this, 0);
+  DWOCU->setRangesSection(RangeSection, DWORangesBase);
   return true;
 }