Don't insert clang include path for host (ELF) executables
Host (ELF) executables like darling, mldr or wrapgen are not built with
-nostdinc, so there's no need to insert clang's include path manually.
On the other hand, cross-compiled darling and mldr may use a different
set of clang includes, which may cause conflicts. For example, Android
NDK uses customized headers in
$NDK/toolchains/llvm/prebuilt/linux-x86_64/lib64/clang/3.8.275480/include/