sys/newlib: Add __attribute__((used)) to _fini
sys/newlib: Add __attribute__((used)) to _fini

No ROM cost, only fixes a linker error with non-nano newlib and LTO enabled.

authmillenon/RIOT,ks156/RIOT,biboc/RIOT,toonst/RIOT,yogo1212/RIOT,kaspar030/RIOT,toonst/RIOT,kbumsik/RIOT,dailab/RIOT,jasonatran/RIOT,adjih/RIOT,OTAkeys/RIOT,biboc/RIOT,alignan/RIOT,katezilla/RIOT,katezilla/RIOT,A-Paul/RIOT,neiljay/RIOT,OTAkeys/RIOT,adrianghc/RIOT,mtausig/RIOT,jbeyerstedt/RIOT-OTA-update,authmillenon/RIOT,tfar/RIOT,rfuentess/RIOT,Josar/RIOT,beurdouche/RIOT,x3ro/RIOT,syin2/RIOT,basilfx/RIOT,immesys/RiSyn,smlng/RIOT,RIOT-OS/RIOT,roberthartung/RIOT,miri64/RIOT,avmelnikoff/RIOT,tfar/RIOT,backenklee/RIOT,Ell-i/RIOT,A-Paul/RIOT,aeneby/RIOT,miri64/RIOT,smlng/RIOT,Hyungsin/RIOT-OS,neumodisch/RIOT,beurdouche/RIOT,BytesGalore/RIOT,altairpearl/RIOT,immesys/RiSyn,TobiasFredersdorf/RIOT,neiljay/RIOT,katezilla/RIOT,rfuentess/RIOT,jbeyerstedt/RIOT-OTA-update,lazytech-org/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,gautric/RIOT,lazytech-org/RIOT,dkm/RIOT,kYc0o/RIOT,BytesGalore/RIOT,beurdouche/RIOT,d00616/RIOT,cladmi/RIOT,gebart/RIOT,thomaseichinger/RIOT,mfrey/RIOT,kb2ma/RIOT,kb2ma/RIOT,RIOT-OS/RIOT,x3ro/RIOT,kaleb-himes/RIOT,authmillenon/RIOT,kbumsik/RIOT,thomaseichinger/RIOT,roberthartung/RIOT,OTAkeys/RIOT,tfar/RIOT,kbumsik/RIOT,OlegHahm/RIOT,neumodisch/RIOT,jasonatran/RIOT,Josar/RIOT,yogo1212/RIOT,gebart/RIOT,kerneltask/RIOT,dailab/RIOT,TobiasFredersdorf/RIOT,authmillenon/RIOT,kaspar030/RIOT,immesys/RiSyn,Hyungsin/RIOT-OS,rfuentess/RIOT,gebart/RIOT,aeneby/RIOT,avmelnikoff/RIOT,neiljay/RIOT,thomaseichinger/RIOT,neumodisch/RIOT,basilfx/RIOT,aeneby/RIOT,miri64/RIOT,rfuentess/RIOT,mfrey/RIOT,smlng/RIOT,tfar/RIOT,plushvoxel/RIOT,OlegHahm/RIOT,toonst/RIOT,Ell-i/RIOT,A-Paul/RIOT,cladmi/RIOT,kaspar030/RIOT,biboc/RIOT,aeneby/RIOT,BytesGalore/RIOT,gautric/RIOT,thomaseichinger/RIOT,altairpearl/RIOT,gebart/RIOT,kerneltask/RIOT,x3ro/RIOT,ks156/RIOT,yogo1212/RIOT,hamilton-mote/RIOT-OS,kbumsik/RIOT,Ell-i/RIOT,lazytech-org/RIOT,katezilla/RIOT,RIOT-OS/RIOT,syin2/RIOT,Ell-i/RIOT,jfischer-phytec-iot/RIOT,backenklee/RIOT,plushvoxel/RIOT,OTAkeys/RIOT,adrianghc/RIOT,dailab/RIOT,josephnoir/RIOT,jfischer-phytec-iot/RIOT,gautric/RIOT,kYc0o/RIOT,A-Paul/RIOT,miri64/RIOT,mfrey/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,alignan/RIOT,kerneltask/RIOT,TobiasFredersdorf/RIOT,smlng/RIOT,plushvoxel/RIOT,kYc0o/RIOT,altairpearl/RIOT,Josar/RIOT,ks156/RIOT,LudwigKnuepfer/RIOT,neiljay/RIOT,d00616/RIOT,mtausig/RIOT,ant9000/RIOT,BytesGalore/RIOT,backenklee/RIOT,miri64/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,adrianghc/RIOT,jfischer-phytec-iot/RIOT,smlng/RIOT,immesys/RiSyn,cladmi/RIOT,x3ro/RIOT,kaleb-himes/RIOT,beurdouche/RIOT,josephnoir/RIOT,cladmi/RIOT,jfischer-phytec-iot/RIOT,avmelnikoff/RIOT,ks156/RIOT,lazytech-org/RIOT,adrianghc/RIOT,tfar/RIOT,ant9000/RIOT,avmelnikoff/RIOT,aeneby/RIOT,cladmi/RIOT,yogo1212/RIOT,jbeyerstedt/RIOT-OTA-update,adrianghc/RIOT,altairpearl/RIOT,LudwigKnuepfer/RIOT,alignan/RIOT,ant9000/RIOT,toonst/RIOT,ant9000/RIOT,authmillenon/RIOT,jbeyerstedt/RIOT-OTA-update,avmelnikoff/RIOT,neumodisch/RIOT,adjih/RIOT,katezilla/RIOT,kaleb-himes/RIOT,ant9000/RIOT,x3ro/RIOT,gautric/RIOT,neumodisch/RIOT,hamilton-mote/RIOT-OS,basilfx/RIOT,biboc/RIOT,adjih/RIOT,kb2ma/RIOT,lazytech-org/RIOT,TobiasFredersdorf/RIOT,kYc0o/RIOT,mtausig/RIOT,kbumsik/RIOT,kYc0o/RIOT,A-Paul/RIOT,yogo1212/RIOT,adjih/RIOT,backenklee/RIOT,kb2ma/RIOT,LudwigOrtmann/RIOT,beurdouche/RIOT,immesys/RiSyn,Hyungsin/RIOT-OS,TobiasFredersdorf/RIOT,dailab/RIOT,RIOT-OS/RIOT,kaleb-himes/RIOT,jasonatran/RIOT,d00616/RIOT,syin2/RIOT,LudwigOrtmann/RIOT,gebart/RIOT,alignan/RIOT,gautric/RIOT,kb2ma/RIOT,plushvoxel/RIOT,rfuentess/RIOT,josephnoir/RIOT,d00616/RIOT,biboc/RIOT,kerneltask/RIOT,mtausig/RIOT,authmillenon/RIOT,OlegHahm/RIOT,jasonatran/RIOT,Josar/RIOT,thomaseichinger/RIOT,ks156/RIOT,dkm/RIOT,kaspar030/RIOT,kaspar030/RIOT,mfrey/RIOT,hamilton-mote/RIOT-OS,BytesGalore/RIOT,kerneltask/RIOT,altairpearl/RIOT,LudwigOrtmann/RIOT,LudwigKnuepfer/RIOT,adjih/RIOT,Josar/RIOT,roberthartung/RIOT,Hyungsin/RIOT-OS,josephnoir/RIOT,Hyungsin/RIOT-OS,toonst/RIOT,josephnoir/RIOT,jfischer-phytec-iot/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,syin2/RIOT,mfrey/RIOT,d00616/RIOT,kaleb-himes/RIOT,immesys/RiSyn,LudwigKnuepfer/RIOT,dkm/RIOT,altairpearl/RIOT,OlegHahm/RIOT,neiljay/RIOT,jasonatran/RIOT,dailab/RIOT,plushvoxel/RIOT,hamilton-mote/RIOT-OS,d00616/RIOT,LudwigOrtmann/RIOT,alignan/RIOT,roberthartung/RIOT,mtausig/RIOT,LudwigKnuepfer/RIOT,hamilton-mote/RIOT-OS,foss-for-synopsys-dwc-arc-processors/RIOT,dkm/RIOT,foss-for-synopsys-dwc-arc-processors/RIOT,dkm/RIOT,neumodisch/RIOT,backenklee/RIOT,basilfx/RIOT,OlegHahm/RIOT,Ell-i/RIOT,roberthartung/RIOT,LudwigOrtmann/RIOT,OTAkeys/RIOT,syin2/RIOT,LudwigOrtmann/RIOT,jbeyerstedt/RIOT-OTA-update,basilfx/RIOT