[asan, myriad] Reset shadow memory during exit
[asan, myriad] Reset shadow memory during exit

Reset shadow memory during exit.  Also update a cut-and-paste comment,
and do some minor refactoring of InitializeShadowMemory.

Differential Revision: https://reviews.llvm.org/D47501

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@333503 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt,llvm-mirror/compiler-rt