CMake, include/:  changes to make fiddle 2.0 better

cmake: remove unused directories from skia.h / ${public_includes}

SkPreConfig.h:  work around buggy `#ifdef linux`

include:  guard many platform-specific headers
CQ_EXTRA_TRYBOTS=client.skia.compile:Build-Ubuntu-GCC-x86_64-Release-CMake-Trybot,Build-Mac10.9-Clang-x86_64-Release-CMake-Trybot

Review URL: https://codereview.chromium.org/1488813002
11 files changed