small fix related to GSL cmake stuff
small fix related to GSL cmake stuff

pasuka/eigen,pasuka/eigen,TSC21/Eigen,cjntaylor/eigen,TSC21/Eigen,ritsu1228/eigen,cjntaylor/eigen,cjntaylor/eigen,Zefz/eigen,ROCmSoftwarePlatform/hipeigen,pasuka/eigen,ROCmSoftwarePlatform/hipeigen,ritsu1228/eigen,pthulhu/eigen,TSC21/Eigen,toastedcrumpets/eigen,TSC21/Eigen,toastedcrumpets/eigen,toastedcrumpets/eigen,pasuka/eigen,cjntaylor/eigen,Zefz/eigen,ritsu1228/eigen,toastedcrumpets/eigen,pthulhu/eigen,pthulhu/eigen,ritsu1228/eigen,ROCmSoftwarePlatform/hipeigen,Zefz/eigen,ROCmSoftwarePlatform/hipeigen,ritsu1228/eigen,Zefz/eigen,pthulhu/eigen,pthulhu/eigen,pasuka/eigen