encoder: use more portable %PRIu64, define __STDC_FORMAT_MACROS

Older GCC versions and clang require __STDC_FORMAT_MACROS to be defined prior to
including stdint.h when compiling for C++, in order for PRIu64 and friends to be
defined
aq: Bug Fixes in aq , ssim when ctu size is not set as 64.

1.Calculate qp offset for CU based maxCuSize set in FrameEncoder::calcQpForCu
2.Fix height for ssim computation based on maxCuHeight in FrameFilter::processRowPost
Fix to eliminate unwanted application of weight in some (ref, enc) pairs
encoder: change default frameNumThreads for 4-core HT CPUs to 3
cmake: gcc flag introspection to fix Mac OS X 10.6 build
presets: modifications to smoothen the performance-efficiency plot.
vec: tab to spaces
Merge with stable