"g++ -o conftest -I../../../.ext/include/x86_64-linux -I../../.././include -I../../.././ext/-test-/cxxanyargs    -g -O2 conftest.cc  -L. -L../../.. -L. -fstack-protector-strong -rdynamic -Wl,-export-dynamic     -Wl,-rpath,/usr/local/rvm/rubies/ruby-2.7.4/lib -L/usr/local/rvm/rubies/ruby-2.7.4/lib -lruby-static -lz -lpthread -lrt -lrt -ldl -lcrypt -lm   -lm   -lc"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return !!argv[argc];
6: }
/* end */

"g++ -I../../../.ext/include/x86_64-linux -I../../.././include -I../../.././ext/-test-/cxxanyargs    -g -O2   -c conftest.cc"
checked program was:
/* begin */
 1: #include "ruby/config.h"
 2: 
 3: namespace {
 4:     typedef int conftest[SIZEOF_LONG == sizeof(long) ? 1 : -1];
 5:     typedef int conftest[SIZEOF_VOIDP == sizeof(void*) ? 1 : -1];
 6: }
 7: 
 8: int
 9: main(int argc, const char** argv)
10: {
11:     return !!argv[argc];
12: }
/* end */

extconf.h is:
/* begin */
1: #ifndef EXTCONF_H
2: #define EXTCONF_H
3: #endif
/* end */