cmake HAVE_ASM_SYMVER examples

ceph/ceph cmake/modules/CephChecks.cmake :184

check_c_source_compiles("
void func_v1() {}
__asm__(\".symver func_v1, func@v1\");
void func_v2() {}
__asm__(\".symver func_v2, func@v2\");

int main() {}"
  HAVE_ASM_SYMVER)