WebAssembly: support imports

C/C++ code can declare an extern function, which will show up as an import in WebAssembly's output. It's expected that the linker will resolve these, and mark unresolved imports as call_import (I have a patch which does this in wasmate).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250875 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed