cpu/stm32: remove use of export for LINKFLAGS
cpu/stm32: remove use of export for LINKFLAGS

OTAkeys/RIOT,miri64/RIOT,kaspar030/RIOT,yogo1212/RIOT,authmillenon/RIOT,miri64/RIOT,basilfx/RIOT,miri64/RIOT,authmillenon/RIOT,authmillenon/RIOT,yogo1212/RIOT,mtausig/RIOT,x3ro/RIOT,josephnoir/RIOT,toonst/RIOT,jasonatran/RIOT,basilfx/RIOT,OlegHahm/RIOT,josephnoir/RIOT,ant9000/RIOT,kYc0o/RIOT,yogo1212/RIOT,yogo1212/RIOT,RIOT-OS/RIOT,basilfx/RIOT,x3ro/RIOT,miri64/RIOT,mtausig/RIOT,ant9000/RIOT,OTAkeys/RIOT,yogo1212/RIOT,smlng/RIOT,x3ro/RIOT,jasonatran/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,OTAkeys/RIOT,toonst/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,x3ro/RIOT,josephnoir/RIOT,authmillenon/RIOT,jasonatran/RIOT,OlegHahm/RIOT,josephnoir/RIOT,mtausig/RIOT,smlng/RIOT,kYc0o/RIOT,kYc0o/RIOT,yogo1212/RIOT,OTAkeys/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,smlng/RIOT,josephnoir/RIOT,miri64/RIOT,ant9000/RIOT,kYc0o/RIOT,ant9000/RIOT,x3ro/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,OlegHahm/RIOT,basilfx/RIOT,kaspar030/RIOT,toonst/RIOT,jasonatran/RIOT,authmillenon/RIOT,smlng/RIOT,mtausig/RIOT,kYc0o/RIOT,toonst/RIOT,kaspar030/RIOT,basilfx/RIOT,RIOT-OS/RIOT,smlng/RIOT,toonst/RIOT,OlegHahm/RIOT,kaspar030/RIOT,mtausig/RIOT