C3: build and run unit tests

Enable building and running of unit tests in CI for C3 as well as fix
related compile errors

Also enables building of C3 test apps

components/mbedtls/test/test_mbedtls_mpi.c

@@ -66,7 +66,7 @@ static void test_bignum_mult_variant(const char *a_str, const char *b_str, const
 
 #ifdef CONFIG_MBEDTLS_HARDWARE_MPI
     /* if mod_bits arg is set, also do a esp_mpi_mul_mod() call */
-    if (mod_bits > 0) {
+    if (mod_bits > 0 && mod_bits <= SOC_RSA_MAX_BIT_LEN) {
         mbedtls_mpi_init(&M);
         for(int i = 0; i < mod_bits; i++) {
             mbedtls_mpi_set_bit(&M, i, 1);