Important: #107328 - $GLOBALS['TCA'] in base TCA files 

See forge#107328

Description 

The backward compatibility for using $GLOBALS['TCA'] in base TCA files has been removed. Base TCA files are the first TCA files loaded by the Core and do not have the fully loaded TCA available yet. Until now, this worked because the Core temporarily populated this global array during the loading process.

Note that the usage of $GLOBALS['TCA'] in base TCA files was never explicitly allowed or disallowed, only discouraged. It worked only due to internal system knowledge by the user, for example, knowing that the loading order of extensions affects when those files are loaded. The only place this array should be used is inside TCA/Overrides/*.php files. For all other cases, the TcaSchema should be preferred.

Migration 

In the uncommon case that you find usages of $GLOBALS['TCA'] in base TCA files, move that access to TCA/Overrides/*.php files instead.