This speeds up dumping make variables from ~380ms using make to ~220ms
using ckati. It also means that we're consistently using the same parser
for builds (with the same .KATI_READONLY/etc extensions).
envsetup.sh (lunch) / other scripts still use make, changing those to go
through soong_ui will be a future change.
Test: m clean; m nothing
Test: USE_GOMA=true m nothing
Test: m PRODUCT-aosp_x86-sdk
Test: m APP-Calculator
Test: build/soong/build_test.bash -only-config (on AOSP and internal master)
Change-Id: I6ca554de8de4955fb869001d06d29969b75751cc