[llgo]: fix compilation under current llvm
Patch rL322965 changed how intrinsics for memset and memzero
were defined. This causes a regression in LLGO making it no
longer buidable. In addition to that one pass was renamed,
so this also addresses the pass naming disparity.
I removed all split stack related bits from this patch as
Differential Revision: https://reviews.llvm.org/D56638