Incorrect LLVM_INCLUDE path (and possibly LLVM_LIBDIR)

[jessymilare]

The path to LLVM include directory is wrong.

julia> Clang.LLVM_LIBDIR
"C:\\Users\\jessy\\.julia\\artifacts\\3135abc6132c4619d21c4edd03e416c2c46e3bec\\bin"

julia> isdir(ans)
true

julia> Clang.LLVM_INCLUDE
"C:\\Users\\jessy\\.julia\\artifacts\\3135abc6132c4619d21c4edd03e416c2c46e3bec\\bin\\clang\\9.0.1\\include"

julia> isdir(ans)
false

Perhaps the correct definition of the constants (in Clang.jl file) should be:

const LLVM_BINDIR = dirname(LibClang.Clang_jll.libclang_path)
const LLVM_LIBDIR = joinpath(dirname(LLVM_BINDIR), "lib")
const LLVM_INCLUDE = joinpath(LLVM_LIBDIR, "clang", LLVM_VERSION, "include")
const CLANG_INCLUDE = LLVM_INCLUDE

[Gnimuc]

Nice catch! I didn't test this on Windows.