[docs] Fix the CMAKE_BUILD_TYPE option in the cmake command in GettingStarted.rst.

[terrydang]

Summary

The cmake command contained a duplicate CMAKE_BUILD_TYPE option in the section "Compiling the LLVM Suite Source Code".

[jhenderson]

LGTM.

[terrydang]

I do not have commit access, could someone commit the change for me?

Name: terrydang
Email: [e-mail]

[jhenderson]

I forgot to add the Differential Revision bit to the commit message. This landed as https://github.com/llvm/llvm-project/commit/3a44c576b146521d14f71fa50e071871623e6655.

llvm/docs/GettingStarted.rst

 ------------------------------------
 
 Unlike with autotools, with CMake your build type is defined at configuration.
 If you want to change your build type, you can re-run cmake with the following
 invocation:
 
    .. code-block:: console
 
-     % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=<type> -DCMAKE_BUILD_TYPE=type SRC_ROOT
+     % cmake -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=<type> SRC_ROOT
 
 Between runs, CMake preserves the values set for all options. CMake has the
 following build types defined:
 
 Debug
 
   These builds are the default. The build system will compile the tools and
   libraries unoptimized, with debugging information, and asserts enabled.