[Docs] Minor Fixups in Advanced Builds Documentation

This patch changes two instances of an ampersand to a written out and
for more consistency with the rest of the file and brevity. In addition,
the last `cmake --build` reference is removed, again for consistency
with the rest of the file which shows the ninja invocations. This cmake
invocation also passed in the `--parallel` flag which doesn't make sense
with ninja using all threads by default.

This was changed in the previous patch to touch this line
(https://reviews.llvm.org/D88990), but if we want to change this, it
should be done across the entire file.