WEBP_HAVE_FLAG_LOCAL -> WEBP_HAVE_FLAG_${WEBP_SIMD_FLAG} this will
include the flag being tested in the output:
-- Performing Test WEBP_HAVE_FLAG_NEON
Change-Id: I1c0a143a857b16e4eb1fcf8b23c176380a5fef29
This will well isolate contributions for original code,
generated code and SIMD (especially for Android).
Change-Id: Ie47664decc7f43c2f57260a72cab951c347281a7