[WebAssembly] Strip threadlocal attribute from globals in single thread mode

The default thread model for wasm is single, and in this mode thread-local
global variables can be lowered identically to non-thread-local variables.

Differential Revision: https://reviews.llvm.org/D44703

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328049 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed