Forward declare OMPClause in Sema.h to avoid an include

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186824 91177308-0d34-0410-b5e6-96231b3b80d8
Install git-clang-format along with clang-format by default.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@186825 91177308-0d34-0410-b5e6-96231b3b80d8