ENH: make possible to switch from system gccxml to EP in cmake gui
ENH: make possible to switch from system gccxml to EP in cmake gui

By default, GCCXML is set to the path of the gccxml built with an
external project. If the user choose to use the system gccxml, cmake
doesn't search for it because GCCXML is already set.
To avoid that, we delete GCCXML if it is equal to the gccxml path in
the external project before trying to find it with the usual
find_package() macro.

Change-Id: I53443b624ab7efa219f28bbacaae948a54dfdd43

hinerm/ITK,jcfr/ITK,zachary-williamson/ITK,hinerm/ITK,heimdali/ITK,malaterre/ITK,hjmjohnson/ITK,malaterre/ITK,PlutoniumHeart/ITK,LucHermitte/ITK,Kitware/ITK,zachary-williamson/ITK,LucasGandel/ITK,cpatrick/ITK-RemoteIO,BlueBrain/ITK,fedral/ITK,rhgong/itk-with-dom,rhgong/itk-with-dom,fedral/ITK,hinerm/ITK,fuentesdt/InsightToolkit-dev,GEHC-Surgery/ITK,BlueBrain/ITK,blowekamp/ITK,biotrump/ITK,LucasGandel/ITK,richardbeare/ITK,vfonov/ITK,fedral/ITK,eile/ITK,jmerkow/ITK,Kitware/ITK,wkjeong/ITK,fedral/ITK,stnava/ITK,LucasGandel/ITK,zachary-williamson/ITK,stnava/ITK,biotrump/ITK,thewtex/ITK,itkvideo/ITK,heimdali/ITK,thewtex/ITK,itkvideo/ITK,wkjeong/ITK,cpatrick/ITK-RemoteIO,LucHermitte/ITK,cpatrick/ITK-RemoteIO,atsnyder/ITK,CapeDrew/DITK,BRAINSia/ITK,paulnovo/ITK,eile/ITK,richardbeare/ITK,itkvideo/ITK,InsightSoftwareConsortium/ITK,cpatrick/ITK-RemoteIO,atsnyder/ITK,msmolens/ITK,fuentesdt/InsightToolkit-dev,biotrump/ITK,Kitware/ITK,cpatrick/ITK-RemoteIO,jcfr/ITK,CapeDrew/DCMTK-ITK,daviddoria/itkHoughTransform,BRAINSia/ITK,biotrump/ITK,ajjl/ITK,LucasGandel/ITK,fbudin69500/ITK,stnava/ITK,fedral/ITK,msmolens/ITK,hjmjohnson/ITK,PlutoniumHeart/ITK,wkjeong/ITK,biotrump/ITK,BlueBrain/ITK,itkvideo/ITK,hjmjohnson/ITK,vfonov/ITK,eile/ITK,LucHermitte/ITK,paulnovo/ITK,hendradarwin/ITK,malaterre/ITK,hjmjohnson/ITK,Kitware/ITK,InsightSoftwareConsortium/ITK,CapeDrew/DCMTK-ITK,zachary-williamson/ITK,stnava/ITK,heimdali/ITK,spinicist/ITK,CapeDrew/DCMTK-ITK,zachary-williamson/ITK,hinerm/ITK,jmerkow/ITK,fbudin69500/ITK,blowekamp/ITK,msmolens/ITK,itkvideo/ITK,PlutoniumHeart/ITK,GEHC-Surgery/ITK,PlutoniumHeart/ITK,vfonov/ITK,LucasGandel/ITK,CapeDrew/DCMTK-ITK,vfonov/ITK,heimdali/ITK,BlueBrain/ITK,jcfr/ITK,spinicist/ITK,CapeDrew/DCMTK-ITK,zachary-williamson/ITK,msmolens/ITK,msmolens/ITK,rhgong/itk-with-dom,richardbeare/ITK,CapeDrew/DITK,jmerkow/ITK,blowekamp/ITK,biotrump/ITK,hendradarwin/ITK,eile/ITK,hendradarwin/ITK,BlueBrain/ITK,rhgong/itk-with-dom,CapeDrew/DITK,rhgong/itk-with-dom,PlutoniumHeart/ITK,malaterre/ITK,LucHermitte/ITK,wkjeong/ITK,thewtex/ITK,jcfr/ITK,rhgong/itk-with-dom,zachary-williamson/ITK,ajjl/ITK,ajjl/ITK,ajjl/ITK,rhgong/itk-with-dom,stnava/ITK,jcfr/ITK,malaterre/ITK,BRAINSia/ITK,wkjeong/ITK,blowekamp/ITK,hinerm/ITK,InsightSoftwareConsortium/ITK,hendradarwin/ITK,jcfr/ITK,GEHC-Surgery/ITK,paulnovo/ITK,eile/ITK,InsightSoftwareConsortium/ITK,fbudin69500/ITK,hjmjohnson/ITK,richardbeare/ITK,daviddoria/itkHoughTransform,blowekamp/ITK,msmolens/ITK,blowekamp/ITK,BlueBrain/ITK,fedral/ITK,spinicist/ITK,CapeDrew/DITK,hinerm/ITK,hjmjohnson/ITK,CapeDrew/DCMTK-ITK,msmolens/ITK,daviddoria/itkHoughTransform,thewtex/ITK,CapeDrew/DITK,richardbeare/ITK,stnava/ITK,LucasGandel/ITK,jcfr/ITK,paulnovo/ITK,GEHC-Surgery/ITK,PlutoniumHeart/ITK,fuentesdt/InsightToolkit-dev,vfonov/ITK,LucHermitte/ITK,hendradarwin/ITK,hendradarwin/ITK,stnava/ITK,msmolens/ITK,fedral/ITK,spinicist/ITK,thewtex/ITK,eile/ITK,jmerkow/ITK,itkvideo/ITK,spinicist/ITK,daviddoria/itkHoughTransform,eile/ITK,malaterre/ITK,daviddoria/itkHoughTransform,BRAINSia/ITK,GEHC-Surgery/ITK,atsnyder/ITK,LucHermitte/ITK,daviddoria/itkHoughTransform,ajjl/ITK,paulnovo/ITK,InsightSoftwareConsortium/ITK,fuentesdt/InsightToolkit-dev,ajjl/ITK,vfonov/ITK,GEHC-Surgery/ITK,CapeDrew/DCMTK-ITK,stnava/ITK,biotrump/ITK,GEHC-Surgery/ITK,fuentesdt/InsightToolkit-dev,LucHermitte/ITK,Kitware/ITK,fbudin69500/ITK,atsnyder/ITK,CapeDrew/DCMTK-ITK,fuentesdt/InsightToolkit-dev,vfonov/ITK,spinicist/ITK,vfonov/ITK,blowekamp/ITK,cpatrick/ITK-RemoteIO,blowekamp/ITK,wkjeong/ITK,biotrump/ITK,paulnovo/ITK,stnava/ITK,heimdali/ITK,CapeDrew/DITK,malaterre/ITK,hjmjohnson/ITK,atsnyder/ITK,jcfr/ITK,spinicist/ITK,atsnyder/ITK,BRAINSia/ITK,spinicist/ITK,malaterre/ITK,rhgong/itk-with-dom,malaterre/ITK,heimdali/ITK,fbudin69500/ITK,BRAINSia/ITK,ajjl/ITK,LucHermitte/ITK,wkjeong/ITK,hinerm/ITK,fbudin69500/ITK,jmerkow/ITK,itkvideo/ITK,wkjeong/ITK,fedral/ITK,richardbeare/ITK,paulnovo/ITK,itkvideo/ITK,jmerkow/ITK,CapeDrew/DITK,jmerkow/ITK,daviddoria/itkHoughTransform,paulnovo/ITK,ajjl/ITK,cpatrick/ITK-RemoteIO,zachary-williamson/ITK,fbudin69500/ITK,daviddoria/itkHoughTransform,hinerm/ITK,heimdali/ITK,hinerm/ITK,hendradarwin/ITK,jmerkow/ITK,Kitware/ITK,eile/ITK,thewtex/ITK,atsnyder/ITK,GEHC-Surgery/ITK,BlueBrain/ITK,fbudin69500/ITK,eile/ITK,atsnyder/ITK,LucasGandel/ITK,CapeDrew/DCMTK-ITK,fuentesdt/InsightToolkit-dev,richardbeare/ITK,PlutoniumHeart/ITK,BRAINSia/ITK,hendradarwin/ITK,fuentesdt/InsightToolkit-dev,heimdali/ITK,thewtex/ITK,PlutoniumHeart/ITK,vfonov/ITK,InsightSoftwareConsortium/ITK,itkvideo/ITK,Kitware/ITK,atsnyder/ITK,cpatrick/ITK-RemoteIO,daviddoria/itkHoughTransform,spinicist/ITK,CapeDrew/DITK,zachary-williamson/ITK,InsightSoftwareConsortium/ITK,CapeDrew/DITK,fuentesdt/InsightToolkit-dev,BlueBrain/ITK,LucasGandel/ITK