Output error when trying to use --auth (-a) for RTI built without -DAUTH=ON

[hokeun]

Add an error message when trying to use the --auth (-a) option for the RTI built without the -DAUTH=ON option. Also fix a minor build warning.

Relevant issue: lf-lang/lingua-franca#1777

[lhstrh]

LGTM!

[hokeun]

This change will make sure that the RTI outputs an error and terminates with return -1 in main (https://github.com/lf-lang/reactor-c/blob/main/core/federated/RTI/rti.c#L67) when it's executed with an authentication option while it's not built with the OpenSSL support, as shown below. I believe this will fail the test when running the SimpleFederatedAuthenticated test with an RTI without OpenSSL (authentication) support.

./test/C/bin/SimpleFederatedAuthenticated
Federate SimpleFederatedAuthenticated in Federation ID '3c1c172f45cb7d2dab5c5ad93c47549fae6fbf815964fa09'
RTI: Federation ID: 3c1c172f45cb7d2dab5c5ad93c47549fae6fbf815964fa09
Error: --auth requires the RTI to be built with the -DAUTH=ON option.

Command-line arguments:

  -i, --id <n>
   The ID of the federation that this RTI will control.

  -n, --number_of_federates <n>
   The number of federates in the federation that this RTI will control.

  -p, --port <n>
   The port number to use for the RTI. Must be larger than 0 and smaller than 65535. Default is 15045.

  -c, --clock_sync [off|init|on] [period <n>] [exchanges-per-interval <n>]
   The status of clock synchronization for this federate.
       - off: Clock synchronization is off.
       - init (default): Clock synchronization is done only during startup.
       - on: Clock synchronization is done both at startup and during the execution.
   Relevant parameters that can be set:
       - period <n>(in nanoseconds): Controls how often a clock synchronization attempt is made
          (period in nanoseconds, default is 5 msec). Only applies to 'on'.
       - exchanges-per-interval <n>: Controls the number of messages that are exchanged for each
          clock sync attempt (default is 10). Applies to 'init' and 'on'.

  -a, --auth Turn on HMAC authentication options.

  -t, --tracing Turn on tracing.

Command given:
RTI -i 3c1c172f45cb7d2dab5c5ad93c47549fae6fbf815964fa09 -a -n 2 -c init exchanges-per-interval 10

#### Launching the federate federate__fed1.
#### Launching the federate federate__fed2.
#### Bringing the RTI back to foreground so it can receive Control-C.
./test/C/bin/SimpleFederatedAuthenticated: line 69: fg: job has terminated
#### Received ERR signal on line 69. Invoking cleanup().
Killing federate 63269.
Killing federate 63270.
#### Killing RTI 63267.
./test/C/bin/SimpleFederatedAuthenticated: line 17: kill: (63267) - No such process

[edwardalee]

LGTM! Thanks for fixing this.