When running with >1 OpenCV thread, KMeans index generation was
non-deterministic because of a RWW race. Issue is resolved by removing
the offending logic from the parallel section.

 * optimize v_lut_deinterleave
 * optimize v_interleave_/pairs/quads/triplets
 * optimize v_lut, use vec_extract instead of aligned store

The Android NDK 16b has a bug that sets the ANDROID_NDK_REVISION
variable incorrectly, generating an unexpected line break in the
middle of the string. This breaks the build as the generated
version_string.inc presents an invalid C string.

Remove leading and trailing line breaks, warns for line breaks in the
middle of 'msg' and escape them before appending to
OPENCV_BUILD_INFO_STR.

Keep `_FILE_OFFSET_BITS` undefined in Android builds.

 - allow cmake to check sanity of vsx aligned ld/st
 - force universal intrinsics v_load_aligned/v_store_aligned
   to failback to unaligned ld/st if cmake runtime vsx aligned test fail