Improve docs on CMake variables and options

* Improve description of IREE-specific CMake Options and Variables
* Add section on Frequently-used CMake Variables
* Add links from building with CMake docs
* Revise style (use sections instead of bullet points)

Closes https://github.com/google/iree/pull/2260

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/iree/pull/2260 from iml130:docs 4f191f0627d1f827f7f0887ad38b086e183a3504
PiperOrigin-RevId: 317737818
diff --git a/docs/GetStarted/getting_started_macos_cmake.md b/docs/GetStarted/getting_started_macos_cmake.md
index 1fc6777..59d22e8 100644
--- a/docs/GetStarted/getting_started_macos_cmake.md
+++ b/docs/GetStarted/getting_started_macos_cmake.md
@@ -78,7 +78,8 @@
 > Tip:<br>
 > &nbsp;&nbsp;&nbsp;&nbsp;The root
 > [CMakeLists.txt](https://github.com/google/iree/blob/master/CMakeLists.txt)
-> file has options for configuring which parts of the project to enable.
+> file has options for configuring which parts of the project to enable.<br>
+> &nbsp;&nbsp;&nbsp;&nbsp;These are further documented in [CMake Options and Variables](cmake_options_and_variables.md).
 
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