Prebuilt clang: add a TARGET_ENABLE_PREBUILT_CLANG flag, which sets TARGET_CLANG_VERSION to msm-3.4

simply setting TARGET_CLANG_VERSION still enables use of prebuilt clang, as before this commit.

Change-Id: Ib8cb6312d9a7f9ffff3e48c5c66bfb80893bcf97
build: updater-script: Fix mount and format commands on F2FS

Change-Id: I3211fdf059eec5e95519faabb2b4a0968b2f69ee
ota_from_target_files: remove duplicate setting of recovery_img

This variable is already set earlier in the script and does not need
to be wrapped inside of the if statement

Change-Id: I91b7f7d2fc911a3910b3df09cff0ca0f44fe7741
releasetools: Fix error text in ota_from_target_files

property isn't the variable name, prop is

Change-Id: I0fc6adddfd51ba9bc79f6559c61cd831203c9e3d
Merge remote-tracking branch 'upstream/kk44' into kk44