Bug 1522735 - Set enable_sslkeylogfile for NSS gyp build r=firefox-build-system-reviewers,erahm,ted

NSS 3.42 added a new build flag, enable_sslkeylogfile, to toggle the
availability of the SSLKEYLOGFILE variable (see Bug 1515236 and Bug 1519209).

Differential Revision: https://phabricator.services.mozilla.com/D17588

--HG--
extra : moz-landing-system : lando

security/moz.build

@@ -81,6 +81,7 @@ gyp_vars['disable_tests'] = 1
 if CONFIG['NSS_DISABLE_DBM']:
     gyp_vars['disable_dbm'] = 1
 gyp_vars['disable_libpkix'] = 1
+gyp_vars['enable_sslkeylogfile'] = 1
 # pkg-config won't reliably find zlib on our builders, so just force it.
 # System zlib is only used for modutil and signtool unless
 # SSL zlib is enabled, which we are disabling immediately below this.