[lld][WebAssembly] Allow linking of pic code into static binaries

Summary: See https://github.com/emscripten-core/emscripten/issues/9013

Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65922

llvm-svn: 368719