cpu/cortexm_common: Use gcc-ar when building with LTO
cpu/cortexm_common: Use gcc-ar when building with LTO

gcc-ar is a wrapper supplied by gcc for properly handling thin LTO objects.

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