cmake AWS_HAVE_AUXV examples

pingcap/tiflash contrib/aws-cmake/AwsFeatureTests.cmake :90

check_c_source_compiles("
#include <sys/auxv.h>
int main() {
#ifdef __linux__
    getauxval(AT_HWCAP);
    getauxval(AT_HWCAP2);
#endif
    return 0;
}" AWS_HAVE_AUXV)