[BUGFIX] Ignore configurable symlinks in structure check

[BUGFIX] Ignore configurable symlinks in structure check

In composer mode the symlinks to index.php and typo3 are configurable
as well as the typo3_src folder is.

Ignore these links in the structure check in composer mode.

Releases: master
Resolves: #68615
Change-Id: Icd2ab595b7d0261e1903d8adfb68b420ef19d4d4
Reviewed-on: http://review.typo3.org/42107
Reviewed-by: Daniel Goerz <ervaude@gmail.com>
Tested-by: Daniel Goerz <ervaude@gmail.com>
Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Benjamin Mack <benni@typo3.org>
Tested-by: Frans Saris <franssaris@gmail.com>