Think there is a little confusion here ... the check does mysql and php checks then goes to 'custom checks' looking for supported versions of utilities/supports that Moodle would use ... curl being one of them.

There's a difference in MAMP (and other locally installed apps like that) in that MAMP provides all supports needed.

On a Mac - what comes natively with a Mac:
Kens-MacBook-Pro:~ ktask$ curl -V
curl 7.43.0 (x86_64-apple-darwin15.0) libcurl/7.43.0 SecureTransport zlib/1.2.5
Protocols: ... ftps ... http https ... imaps ... ldaps ... pop3s ... smbs ... smtps ...

In /Applications/MAMP/Library/bin
Kens-MacBook-Pro:bin ktask$ ./curl -V
curl 7.28.1 (x86_64-apple-darwin10.8.0) libcurl/7.28.1 OpenSSL/0.9.8} zlib/1.2.8 libidn/1.17

One can see that the curl that comes as port of MAMP is actually older than the curl that's with the OS but it's still a version that Moodle check won't complain about.

This is  one of those areas where running a local (MAMP/XAMP or whatever) *isn't* the same as what a server runs.

On a true server:  CentOS release 6.8 (Final)
Moodle 3.1.highest
Environment Check
Does not report the TLS library issue.

The environment.xml file ... at the very bottom has:

      <CUSTOM_CHECK file="lib/upgradelib.php" function="check_libcurl_version" level="optional">
        <FEEDBACK>
          <ON_CHECK message="libcurlwarning" />
        </FEEDBACK>
      </CUSTOM_CHECK>

the lib/upgradelib.php file ... at the very bottom:

/**
 * Check if recommended version of libcurl is installed or not.
 *
 * @param environment_results $result object to update, if relevant.
 * @return environment_results|null updated results or null.
 */
function check_libcurl_version(environment_results $result) {

    // Supported version and version number.
    $supportedversion = 0x071304;
    $supportedversionstring = "7.19.4";

    // Installed version.
    $curlinfo = curl_version();
    $currentversion = $curlinfo['version_number'];

    if ($currentversion < $supportedversion) {
        // Test fail.
        // Set info, we want to let user know how to resolve the problem.
        $result->setInfo('Libcurl version check');
        $result->setNeededVersion($supportedversionstring);
        $result->setCurrentVersion($curlinfo['version']);
        $result->setStatus(false);
        return $result;
    }

    return null;
}

In the enviroment.xml file of a 3.2 there is an additional check.

Towards the bottom where the other checks reside:

      <CUSTOM_CHECK file="lib/upgradelib.php" function="check_tls_libraries" level="optional">
        <FEEDBACK>
          <ON_CHECK message="tlswarning" />
        </FEEDBACK>
      </CUSTOM_CHECK>
      <CUSTOM_CHECK file="lib/upgradelib.php" function="check_libcurl_version" level="optional">
        <FEEDBACK>
          <ON_CHECK message="libcurlwarning" />
        </FEEDBACK>
      </CUSTOM_CHECK>

On can see there are two separate checks ... a TLS and a LibCurl

> curl -V
curl 7.19.7 (x86_64-redhat-linux-gnu) libcurl/7.19.7 NSS/3.21 Basic ECC zlib/1.2.3 libidn/1.18 libssh2/1.4.2
Protocols: .... https ... scp sftp

Think the issue has to do with what protocols curl can use ... openssl/SSL/https stuff having issues recently it appears that many are now using TLS.

On a local host MAMP/other similar type designed to install easy and run locally ... not shared on the network, etc. by default, it installs using http:// ... no SSL nor TLS certificate required or used.

Basically, until the OS or OS as provided by provider gets updated libraries then Moodle will 'complain' ... but it's not a 'show stopper' - is it?   Should one be concerned ... uhhh, yes, but this isn't like a zero day flaw ... I don't think.

Am not a security expert ... just sharing what I've 'dug out' and offered 2 cent opinion.   Would be nice if a true Moodle.org security expert would shed some light. ;)

'spirit of sharing', Ken

I'm following this post as I just moved an upgraded version on MAMP to the production server and received the notice on the production site. (Moodle 3.2+ and php 7.0.14)

Additionally, we are also current on the libraries (courtesy of our host company-I can never thank them enough):

root@host [~]# cat /etc/redhat-release
CentOS Linux release 7.3.1611 (Core)
root@host [~]# rpm -qa|grep ^openssl
openssl-devel-1.0.1e-60.el7.x86_64
openssl-libs-1.0.1e-60.el7.x86_64
openssl-1.0.1e-60.el7.x86_64
--


I also verified that latest cURL provided by CentOS is installed. 
--
root@host [~]# curl -V
curl 7.29.0 (x86_64-redhat-linux-gnu) libcurl/7.29.0 NSS/3.21 Basic ECC zlib/1.2.7 libidn/1.28 libssh2/1.4.3
Protocols: dict file ftp ftps gopher http https imap imaps ldap ldaps pop3 pop3s rtsp scp sftp smtp smtps telnet tftp 
Features: AsynchDNS GSS-Negotiate IDN IPv6 Largefile NTLM NTLM_WB SSL libz unix-sockets 
--


Along with the PHP module. 
--
root@host [~]# scl enable ea-php54 'php -m"|grep curl
> ^C
root@host [~]# scl enable ea-php54 'php -m'|grep curl
curl
root@host [~]# scl enable ea-php55 'php -m'|grep curl
curl
root@host [~]# scl enable ea-php56 'php -m'|grep curl
curl
root@host [~]# scl enable ea-php70 'php -m'|grep curl
curl
root@host [~]# scl enable ea-php71 'php -m'|grep curl
curl
--