libtommath protects the inclusion of functions by wrapping their
declarations by CPP #ifdef tests and defining the matching macros
within libtommath_class.h.
Add missing macros:
BN_MP_FIND_PRIME_C
BN_MP_ISPRIME_C
Change-Id: Ic577300114f8e88d7a3af3d9f717a249d57f03b1