/usr/include/llvm-c-6.0/ is in llvm-6.0-dev 1:6.0-1ubuntu2.
This file is owned by root:root, with mode 0o755.
..
/usr/include/llvm-c-6.0/llvm-c/
/usr/include/llvm-c-6.0/llvm-c/Analysis.h
/usr/include/llvm-c-6.0/llvm-c/BitReader.h
/usr/include/llvm-c-6.0/llvm-c/BitWriter.h
/usr/include/llvm-c-6.0/llvm-c/Core.h
/usr/include/llvm-c-6.0/llvm-c/DebugInfo.h
/usr/include/llvm-c-6.0/llvm-c/Disassembler.h
/usr/include/llvm-c-6.0/llvm-c/ErrorHandling.h
/usr/include/llvm-c-6.0/llvm-c/ExecutionEngine.h
/usr/include/llvm-c-6.0/llvm-c/IRReader.h
/usr/include/llvm-c-6.0/llvm-c/Initialization.h
/usr/include/llvm-c-6.0/llvm-c/LinkTimeOptimizer.h
/usr/include/llvm-c-6.0/llvm-c/Linker.h
/usr/include/llvm-c-6.0/llvm-c/Object.h
/usr/include/llvm-c-6.0/llvm-c/OrcBindings.h
/usr/include/llvm-c-6.0/llvm-c/Support.h
/usr/include/llvm-c-6.0/llvm-c/Target.h
/usr/include/llvm-c-6.0/llvm-c/TargetMachine.h
/usr/include/llvm-c-6.0/llvm-c/Transforms/
/usr/include/llvm-c-6.0/llvm-c/Transforms/IPO.h
/usr/include/llvm-c-6.0/llvm-c/Transforms/PassManagerBuilder.h
/usr/include/llvm-c-6.0/llvm-c/Transforms/Scalar.h
/usr/include/llvm-c-6.0/llvm-c/Transforms/Vectorize.h
/usr/include/llvm-c-6.0/llvm-c/Types.h
/usr/include/llvm-c-6.0/llvm-c/lto.h