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/ternary.cpp

@@ -13,7 +13,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
+
 #include "function_list.h"
+#include "test_functions.h"
 #include "utility.h"
 
 #include <string.h>
@@ -21,13 +23,6 @@
 #define CORRECTLY_ROUNDED 0
 #define FLUSHED 1
 
-int TestFunc_Float_Float_Float_Float(const Func *f, MTdata, bool relaxedMode);
-int TestFunc_Double_Double_Double_Double(const Func *f, MTdata,
-                                         bool relaxedMode);
-
-extern const vtbl _ternary = { "ternary", TestFunc_Float_Float_Float_Float,
-                               TestFunc_Double_Double_Double_Double };
-
 static int BuildKernel(const char *name, int vectorSize, cl_kernel *k,
                        cl_program *p, bool relaxedMode)
 {