COMP: Update gccxml

Fixes the following warnings in WrapITK:
Policy CMP0048 is not set
Policy CMP0026 is not set
Policy CMP0046 is not set

See:
https://github.com/gccxml/gccxml/commit/a452067b91b890f7027f04beeea7155c1ad6b850
https://github.com/gccxml/gccxml/commit/3eb4078017ae4b95d6f69647068718a5ca890396
https://github.com/gccxml/gccxml/commit/48b49a6954310efc5a79dd1fbc55128fa9b38fb1

Change-Id: Id5e53208110298317129be52815422d752b22703
Merge topic 'BumpGCCXML'

621904fa COMP: Update gccxml