Regroup vtbl definitions to one translation unit (#1167)

Move function declarations to a new header file, with relevant existing
documentation.

Signed-off-by: Marco Antognini <marco.antognini@arm.com>

test_conformance/math_brute_force/reference_math.cpp

@@ -13,6 +13,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+
 #include "harness/compat.h"
 #include "reference_math.h"
 #include <limits.h>