Move crt sources out of API specific directories.

We use one set of sources for all API levels, and the code to find
these made checkbuild.py messier than it needed to be. Move them into
a non-API level specific location.

Test: ndk/checkbuild.py && ndk/run_tests.py
Bug: None
Change-Id: I8e571037b761ebc64b0bf234abd90511778f3224
(cherry picked from commit 3afdb24aa7beeeb206db9d082b1fc496cef35d72)
38 files changed