PR #95959: Include math.h in elementwise.cc

Imported from GitHub PR tensorflow/tensorflow#95959

This is required to build with the most recent version of LLVM's libc++, which moved the `abs` function from `stdlib.h` to `math.h` in llvm/llvm-project#139586.
Copybara import of the project:

--
2fa2ab36dae8afc9cf838a5ce1726e4ba48afec6 by Devon Loehr <[email protected]>:

Include math.h in elementwise.cc

Merging this change closes #95959

FUTURE_COPYBARA_INTEGRATE_REVIEW=tensorflow/tensorflow#95959 from DKLoehr:math 2fa2ab36dae8afc9cf838a5ce1726e4ba48afec6
PiperOrigin-RevId: 775719122

Author: DKLoehr

tflite/kernels/elementwise.cc

@@ -13,6 +13,7 @@ See the License for the specific language governing permissions and
 limitations under the License.
 ==============================================================================*/
 
+#include <math.h>
 #include <stdint.h>
 #include <stdlib.h>