[llvm][docs] Improve formatting of ENABLE_PROJECTS/RUNTIMES description

* Add line breaks so it's clear what should be passed to CMake.
* Make the note into an RST note block.
* Fix a couple of markdown style plain text markers.

Author: DavidSpickett

llvm/docs/CMake.rst

@@ -571,10 +571,12 @@ enabled sub-projects. Nearly all of these variable names begin with
   Semicolon-separated list of projects to build, or *all* for building all
   (clang, lldb, lld, polly, etc) projects. This flag assumes that projects
   are checked out side-by-side and not nested, i.e. clang needs to be in
-  parallel of llvm instead of nested in `llvm/tools`. This feature allows
+  parallel of llvm instead of nested in ``llvm/tools``. This feature allows
   to have one build for only LLVM and another for clang+llvm using the same
   source checkout.
+
   The full list is:
+
   ``clang;clang-tools-extra;cross-project-tests;libc;libclc;lld;lldb;openmp;polly;pstl``
 
 **LLVM_ENABLE_RTTI**:BOOL
@@ -586,10 +588,16 @@ enabled sub-projects. Nearly all of these variable names begin with
   It will build the builtins separately from the other runtimes to preserve
   correct dependency ordering. If you want to build the runtimes using a system
   compiler, see the `libc++ documentation <https://libcxx.llvm.org/BuildingLibcxx.html>`_.
-  Note: the list should not have duplicates with `LLVM_ENABLE_PROJECTS`.
+
+  .. note::
+    The list should not have duplicates with ``LLVM_ENABLE_PROJECTS``.
+
   The full list is:
+
   ``compiler-rt;libc;libcxx;libcxxabi;libunwind;openmp``
+
   To enable all of them, use:
+
   ``LLVM_ENABLE_RUNTIMES=all``
 
 **LLVM_ENABLE_SPHINX**:BOOL