sys/targets: add support for gcc&clang at the same time
sys/targets: add support for gcc&clang at the same time

Add GetEx function that allow to specify gcc/clang.

Update #2171

xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller