OSL 1.10.10

Release 1.10.10 -- 9 May 2020 (compared to 1.10.9)

• Support for building against LLVM 10.0. #1128 #1162
  Note that LLVM 10 can only be used if you are building OSL with C++14
  or newer.
• Change default of OSL_BUILD_MATERIALX to OFF. This will probably be
  deprecated entirely for 1.11's (or 2.0's) final release. But in the mean
  time, we have drifted out of sync with MX, which has their own copies of
  this now, so we're disabling building of these shaders by default.