Add guard for MBEDTLS_ECP_INTERNAL_ALT

MBEDTLS_ECP_RESTARTABLE and MBEDTLS_ECP_INTERNAL_ALT are mutually
exclusive, can't work and shouldn't be compiled together.

Author: yanesca

include/mbedtls/check_config.h

@@ -114,6 +114,7 @@
       defined(MBEDTLS_ECDSA_SIGN_ALT)          || \
       defined(MBEDTLS_ECDSA_VERIFY_ALT)        || \
       defined(MBEDTLS_ECDSA_GENKEY_ALT)        || \
+      defined(MBEDTLS_ECP_INTERNAL_ALT)        || \
       defined(MBEDTLS_ECP_ALT) )
 #error "MBEDTLS_ECP_RESTARTABLE defined, but it cannot coexist with an alternative ECP implementation"
 #endif