have_struct_member: checking for struct stat.st_birthtimespec in sys/stat.h... -------------------- no

"gcc -o conftest -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/pathname    -O3 -ggdb3 -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wno-tautological-compare -Wno-parentheses-equality -Wno-constant-logical-operand -Wno-self-assign -Wunused-variable -Wimplicit-int -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -Wdeprecated-declarations -Wmisleading-indentation -Wno-packed-bitfield-compat -Wsuggest-attribute=noreturn -Wsuggest-attribute=format -Wimplicit-fallthrough=0 -Wduplicated-cond -Wrestrict  -fPIC conftest.c  -L. -L../.. -L. -fstack-protector -rdynamic -Wl,-export-dynamic     -Wl,-rpath,/usr/local/rvm/rubies/ruby-2.5.9/lib -L/usr/local/rvm/rubies/ruby-2.5.9/lib -lruby-static  -lpthread -ldl -lcrypt -lm   -lc"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: int main(int argc, char **argv)
4: {
5:   return 0;
6: }
/* end */

"gcc -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/pathname    -O3 -ggdb3 -Wall -Wextra -Wno-unused-parameter -Wno-parentheses -Wno-long-long -Wno-missing-field-initializers -Wno-tautological-compare -Wno-parentheses-equality -Wno-constant-logical-operand -Wno-self-assign -Wunused-variable -Wimplicit-int -Wpointer-arith -Wwrite-strings -Wdeclaration-after-statement -Wimplicit-function-declaration -Wdeprecated-declarations -Wmisleading-indentation -Wno-packed-bitfield-compat -Wsuggest-attribute=noreturn -Wsuggest-attribute=format -Wimplicit-fallthrough=0 -Wduplicated-cond -Wrestrict  -fPIC   -c conftest.c"
conftest.c:6:35: error: ‘struct stat’ has no member named ‘st_birthtimespec’
 int s = (char *)&((struct stat*)0)->st_birthtimespec - (char *)0;
                                   ^~
cc1: warning: unrecognized command line option ‘-Wno-self-assign’
cc1: warning: unrecognized command line option ‘-Wno-constant-logical-operand’
cc1: warning: unrecognized command line option ‘-Wno-parentheses-equality’
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: #include <sys/stat.h>
 4: 
 5: /*top*/
 6: int s = (char *)&((struct stat*)0)->st_birthtimespec - (char *)0;
 7: int main(int argc, char **argv)
 8: {
 9:   return 0;
10: }
/* end */

--------------------

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