makefiles/scan-build: Produce an error when doing 'scan-build-analyze'
makefiles/scan-build: Produce an error when doing 'scan-build-analyze'

This makes doing 'scan-build-analyze' produce an error at execution if
WERROR=1.

When used from `scan-build` it will not procude an error to display the result
webpage.

ant9000/RIOT,smlng/RIOT,OTAkeys/RIOT,ant9000/RIOT,rfuentess/RIOT,basilfx/RIOT,kYc0o/RIOT,kaspar030/RIOT,gebart/RIOT,biboc/RIOT,biboc/RIOT,BytesGalore/RIOT,basilfx/RIOT,josephnoir/RIOT,mtausig/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,authmillenon/RIOT,yogo1212/RIOT,basilfx/RIOT,basilfx/RIOT,ant9000/RIOT,yogo1212/RIOT,kaspar030/RIOT,mfrey/RIOT,kaspar030/RIOT,kaspar030/RIOT,OlegHahm/RIOT,cladmi/RIOT,jasonatran/RIOT,jasonatran/RIOT,biboc/RIOT,smlng/RIOT,OTAkeys/RIOT,gebart/RIOT,smlng/RIOT,kYc0o/RIOT,ant9000/RIOT,lazytech-org/RIOT,aeneby/RIOT,OlegHahm/RIOT,toonst/RIOT,miri64/RIOT,mfrey/RIOT,x3ro/RIOT,ant9000/RIOT,mtausig/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,toonst/RIOT,A-Paul/RIOT,rfuentess/RIOT,kYc0o/RIOT,lazytech-org/RIOT,mfrey/RIOT,rfuentess/RIOT,mfrey/RIOT,cladmi/RIOT,BytesGalore/RIOT,mtausig/RIOT,smlng/RIOT,miri64/RIOT,BytesGalore/RIOT,josephnoir/RIOT,lazytech-org/RIOT,gebart/RIOT,biboc/RIOT,jasonatran/RIOT,gebart/RIOT,rfuentess/RIOT,lazytech-org/RIOT,yogo1212/RIOT,authmillenon/RIOT,OlegHahm/RIOT,smlng/RIOT,rfuentess/RIOT,A-Paul/RIOT,toonst/RIOT,OTAkeys/RIOT,mtausig/RIOT,miri64/RIOT,yogo1212/RIOT,josephnoir/RIOT,josephnoir/RIOT,aeneby/RIOT,yogo1212/RIOT,x3ro/RIOT,OlegHahm/RIOT,gebart/RIOT,aeneby/RIOT,miri64/RIOT,cladmi/RIOT,toonst/RIOT,mfrey/RIOT,aeneby/RIOT,BytesGalore/RIOT,RIOT-OS/RIOT,biboc/RIOT,authmillenon/RIOT,mtausig/RIOT,RIOT-OS/RIOT,A-Paul/RIOT,OlegHahm/RIOT,kaspar030/RIOT,x3ro/RIOT,RIOT-OS/RIOT,lazytech-org/RIOT,yogo1212/RIOT,aeneby/RIOT,A-Paul/RIOT,RIOT-OS/RIOT,josephnoir/RIOT,authmillenon/RIOT,x3ro/RIOT,A-Paul/RIOT,kYc0o/RIOT,cladmi/RIOT,authmillenon/RIOT,cladmi/RIOT,basilfx/RIOT,toonst/RIOT,kYc0o/RIOT,miri64/RIOT,BytesGalore/RIOT,jasonatran/RIOT,authmillenon/RIOT,x3ro/RIOT