This target is required so files for header-only libs
show up in Qt Creator. So far it was just a custom target.
However, this way include directories and build flags are
not correctly passed to the code model. So creating an
actual library now.
Seems like the trick with the three dots isn't working
with GCC 8 anymore. So let's make it a default template
Not sure whether GCC 8 is here correct and whether this
workaround causes further trouble.
6.4 has been release after 20170502 but still throws
ios_base::failure with old ABI. It is not a good idea
to use the timestamp to distinguish release versions.
Note that _GLIBCXX_RELEASE is not defined in older
GCC versions. But if the macro is not present, we also
know that it will throw the old version.