[asan] Explicitly declare memintrinsics interceptors to have C linkage
[asan] Explicitly declare memintrinsics interceptors to have C linkage

This is needed on RTEMS.  Also update a comment.

Differential Revision: https://reviews.llvm.org/D47079

git-svn-id: c199f293c43da69278bea8e88f92242bf3aa95f7@332746 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