Migrate known build issues from BUILD.md in core repo

[dalg24]

See kokkos/kokkos#8242

Pasting below what we had in BUILD.md

Known Issues

Cray

• The Cray compiler wrappers do static linking by default. This seems to break the Kokkos build. You will likely need to set the environment > variable CRAYPE_LINK_TYPE=dynamic in order to link correctly. Kokkos warns during configure if this is missing.
• The Cray compiler identifies to CMake as Clang, but it sometimes has its own flags that differ from Clang. We try to include all exceptions, but flag errors may occur in which a Clang-specific flag is passed that the Cray compiler does not recognize.

Fortran

• In a mixed C++/Fortran code, CMake will use the C++ linker by default. If you override this behavior and use Fortran as the link language, the link may break because Kokkos adds linker flags expecting the linker to be C++. Prior to CMake 3.18, Kokkos has no way of detecting in downstream projects that the linker was changed to Fortran. From CMake 3.18, Kokkos can use generator expressions to avoid adding flags when the linker is not C++. Note: Kokkos will not add any linker flags in this Fortran case. The user will be entirely on their own to add the appropriate linker flags.

Are these still relevant?
If so they need to be added to docs/source/known-issues.rst