OSL 1.10.11

Release 1.10.11 -- 1 Jun 2020 (compared to 1.10.10)

• Fixes to support building against LLVM 9 on some distributions. #1171
• When building against LLVM 10, enforce requirement for C++14 with
  appropriate warning when using C++11. #1135
• Switch to using CMAKE_CXX_STANDARD as the main way to request particular
  C++ standard versions. (USE_CPP should continue to work, though.)
• Fixes to MINGW compile, and make sure all stream file I/O is UTF-8 safe.
  #1188