[msan] Allow nested symbolizer and loader scopes.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@191196 91177308-0d34-0410-b5e6-96231b3b80d8
[msan] Fix a WTF in r191196.


git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@191197 91177308-0d34-0410-b5e6-96231b3b80d8