On the macOS deps builder, if certain libraries were installed
system-wide using Homebrew, they could be prioritized during the
linking of dependencies over our own versions, causing breakages
when running the built libraries on other systems.
For OpenColorIO, homebrew Imath could be linked if installed.
For TIFF (& libjpeg as a transitive dep), homebrew libdeflate
could be linked if installed.
This commit fixes both of these issues by directly specifying the
library path to prevent the linker from wrongly inferring it to a
system-wide path.
918db88a34