Investigate Clang Bugs

[mmha]

When using modules in clang 5.0 svn, Hana iterates over wrong structs. For example, the test Buffer_WithData fails, because parse(Buffer) iterates over Accessor instead.

Also, calling clang-tidy with modules enabled causes a segmentation fault:

$ CC=clang CXX=clang++ cmake .. -DGLTFPP_BUILD_TESTS=1 -DGLTFPP_ENABLE_MODULES=1
$ clang-tidy -p=. ../test/glTF.cpp
[1]    32459 segmentation fault (core dumped)  clang-tidy -p=. ../test/glTF.cpp