CMake: set stack size for MSVC in just one place

After r192904, Reid pointed out he thought we already set the stack
size for MSVC. Turns out we did, but it didn't seem to work.

This commit sets the stack size in a single place, using
CMAKE_EXE_LINKER_FLAGS because that seems to be the way that works
best.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@192912 91177308-0d34-0410-b5e6-96231b3b80d8