1. Add -Wno-error=unknown flag to clang-format. (details)
Commit f64903fd81764f1fde7aeb00eea5e1d488458f63 by joachim
Add -Wno-error=unknown flag to clang-format.

Currently newer clang-format options cannot be included in .clang-format files, if not all users can be forced to use an updated version.
This patch tries to solve this by adding an option to clang-format, enabling to ignore unknown (newer) options.

Differential Revision:
The file was modifiedclang/unittests/Format/FormatTest.cpp
The file was modifiedllvm/include/llvm/Support/YAMLTraits.h
The file was modifiedclang/tools/clang-format/ClangFormat.cpp
The file was modifiedclang/docs/ClangFormat.rst
The file was modifiedllvm/include/llvm/Support/YAMLParser.h
The file was modifiedclang/lib/Format/Format.cpp
The file was modifiedllvm/lib/Support/YAMLParser.cpp
The file was modifiedllvm/unittests/ObjectYAML/YAMLTest.cpp
The file was modifiedllvm/lib/Support/YAMLTraits.cpp
The file was modifiedclang/include/clang/Format/Format.h