[PCH] Fix memory leak related to deserialized MacroInfo objects.

Deserialized MacroInfos were not destroyed and if their SmallVector did heap allocation,
it was leaked.

rdar://13768967

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@180771 91177308-0d34-0410-b5e6-96231b3b80d8