Allow PLATFORM_BASE_OS override from product config

PLATFORM_BASE_OS is used to set value for
ro.build.version.base_os which is used to qualify
a device build as SMR (Security Maintenance Release)
during APFE (Android Partner Approval) to optimize the test span.
See ag/26859560 on how we plan to use this variable.

Add PRODUCT_BASE_OS that can be used to override
PLATFORM_BASE_OS value before making it read_only.

Plan is to set the value for PRODUCT_BASE_OS using build flags.
This way, it can be easily set per device when making on-demand
SMR releases. In future, move it to be set via soong variable
during build process once build system side is ready.

Test: None
Bug: 155105803
(cherry picked from https://android-review.googlesource.com/q/commit:c4baa3aa7240e1b0cb013f853669aa419e55ee1e)
Merged-In: I7c4a1f291bb426ad599e1dc937e6ecd3889b5820
Change-Id: I7c4a1f291bb426ad599e1dc937e6ecd3889b5820
3 files changed
tree: 11855c78bcd304ff203c7dedde28506869ecdb32
  1. ci/
  2. common/
  3. core/
  4. packaging/
  5. target/
  6. teams/
  7. tests/
  8. tools/
  9. .gitignore
  10. Android.bp
  11. banchanHelp.sh
  12. buildspec.mk.default
  13. Changes.md
  14. CleanSpec.mk
  15. cogsetup.sh
  16. Deprecation.md
  17. envsetup.sh
  18. help.sh
  19. navbar.md
  20. OWNERS
  21. PREUPLOAD.cfg
  22. rbesetup.sh
  23. README.md
  24. shell_utils.sh
  25. tapasHelp.sh
  26. Usage.txt
README.md

Android Make Build System

This is the Makefile-based portion of the Android Build System.

For documentation on how to run a build, see Usage.txt

For a list of behavioral changes useful for Android.mk writers see Changes.md

For an outdated reference on Android.mk files, see build-system.html. Our Android.mk files look similar, but are entirely different from the Android.mk files used by the NDK build system. When searching for documentation elsewhere, ensure that it is for the platform build system -- most are not.

This Makefile-based system is in the process of being replaced with Soong, a new build system written in Go. During the transition, all of these makefiles are read by Kati, and generate a ninja file instead of being executed directly. That's combined with a ninja file read by Soong so that the build graph of the two systems can be combined and run as one.