I see
/net/usr.work/d003504/Workspace/OpenJDK/jdk/jdk/src/hotspot/share/oops/arrayOop.hpp:141:17: error: comparison is always true due to limited range of data type [-Werror=type-limits]
     assert(type >= 0 && type < T_CONFLICT, "wrong type");
            ~~~~~^~~~

At least on linux x86_64 and on linux s390x, using gcc8.

Reason:
In share/utilities/globalDefinitions.hpp, this modification
- enum BasicType {
+ enum BasicType : u1 {
forced BasicType to be unsigned. As a consequence, at least the above comparison is always true.