Merge "More documentation for C++ global config." into main am: eae6635a

Original change: https://android-review.googlesource.com/c/platform/build/soong/+/2770218



Change-Id: Iea1588705a75630c398bda2931123e6df94022a4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>