Not finding path for standard library

[sean-parent]

Describe the bug Executing a command like the following:

hyde ./include/psutil/safe_cast.hpp -hyde-src-root=../../include -hyde-yaml-dir=../../docs/include \
    -resource-dir=`clang++ --print-resource-dir` -access-filter-protected \
    -namespace-blacklist="safe_cast_detail" -hyde-update -- \
    -x c++ -std=c++14 -stdlib=libc++

Will error out trying to include any file in libc++. The workaround is to explicitly add the path:

 -I`xcode-select --print-path`/usr/include/c++/v1