Update C++ autobuild documentation (#48244)

Co-authored-by: mc <[email protected]>
Co-authored-by: Ben Ahmady <[email protected]>

Author: 3 people

content/code-security/code-scanning/creating-an-advanced-setup-for-code-scanning/codeql-code-scanning-for-compiled-languages.md

@@ -96,7 +96,14 @@ On Linux and macOS, the `autobuild` step reviews the files present in the reposi
 1. If none are found, search subdirectories for a unique directory with a build system for C/C++.
 1. Run an appropriate command to configure the system.
 
-For self-hosted runners, you will likely need to install the `gcc` compiler, and specific projects may also require access to `clang` or `msvc` executables. You will also need to install the build system (for example `msbuild`, `make`, `cmake`, `bazel`) and utilities (such as `python`, `perl`, `lex`, and `yacc`) that your projects depend on.
+{% ifversion codeql-cpp-autoinstall-dependencies %}
+On Ubuntu Linux runners, `autobuild` may try to automatically install dependencies required by the detected configuration and build steps. By default, this behavior is enabled on {% data variables.product.prodname_dotcom %}-hosted runners and disabled on self-hosted runners. You can enable or disable this feature explicitly by setting `CODEQL_EXTRACTOR_CPP_AUTOINSTALL_DEPENDENCIES` to `true` or `false` in the environment. For more information about defining environment variables, see "[AUTOTITLE](/actions/learn-github-actions/variables#defining-environment-variables-for-a-single-workflow)."
+{% endif %}
+
+For self-hosted runners{% ifversion codeql-cpp-autoinstall-dependencies %}, unless automatic installation of dependencies is enabled{% endif %}, you will likely need to install the `gcc` compiler, and specific projects may also require access to `clang` or `msvc` executables. You will also need to install the build system (for example `msbuild`, `make`, `cmake`, `bazel`) and utilities (such as `python`, `perl`, `lex`, and `yacc`) that your projects depend on.
+{%- ifversion codeql-cpp-autoinstall-dependencies %}
+If you enable automatic installation of dependencies, you must ensure that the runner is using Ubuntu and that it can run `sudo apt-get` without requiring a password.
+{%- endif %}
 
 ### `autobuild` for C#
 

data/features/codeql-cpp-autoinstall-dependencies.yml

@@ -0,0 +1,5 @@
+versions:
+  fpt: '*'
+  ghec: '*'
+  ghes: '>3.10'
+  ghae: '>3.10'