linuxkpi: Add overflow.h

Only add check_add_overflow and check_mul_overflow as those are the only
two needed function by DRM v5.3.
Both gcc and clang have builtin to do this check so use them directly
but throw an error if the compiler/code checker doesn't support this builtin.

Sponsored-by: The FreeBSD Foundation
Reviewed by: hselsasky
Differential Revision: https://reviews.freebsd.org/D25015