have_library: checking for deflateReset() in -lz... -------------------- yes

"gcc -o conftest -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC conftest.c  -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 */

"gcc -o conftest -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC conftest.c  -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  -lz  -lm   -lc"
conftest.c: In function ‘t’:
conftest.c:14:57: error: ‘deflateReset’ undeclared (first use in this function)
 int t(void) { void ((*volatile p)()); p = (void ((*)()))deflateReset; return !p; }
                                                         ^~~~~~~~~~~~
conftest.c:14:57: note: each undeclared identifier is reported only once for each function it appears in
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     int (* volatile tp)(void)=(int (*)(void))&t;
 9:     printf("%d", (*tp)());
10:   }
11: 
12:   return !!argv[argc];
13: }
14: int t(void) { void ((*volatile p)()); p = (void ((*)()))deflateReset; return !p; }
/* end */

"gcc -o conftest -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC conftest.c  -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  -lz  -lm   -lc"
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: /*top*/
 4: extern int t(void);
 5: int main(int argc, char **argv)
 6: {
 7:   if (argc > 1000000) {
 8:     int (* volatile tp)(void)=(int (*)(void))&t;
 9:     printf("%d", (*tp)());
10:   }
11: 
12:   return !!argv[argc];
13: }
14: extern void deflateReset();
15: int t(void) { deflateReset(); return 0; }
/* end */

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

have_header: checking for zlib.h... -------------------- yes

"gcc -E -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC  conftest.c -o conftest.i"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <zlib.h>
/* end */

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

checking for kind of operating system... Unix
have_func: checking for crc32_combine() in zlib.h... -------------------- yes

"gcc -o conftest -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC conftest.c  -L. -L../.. -L. -fstack-protector-strong -rdynamic -Wl,-export-dynamic    -lz  -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  -lz  -lm   -lc"
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: #include <zlib.h>
 4: 
 5: /*top*/
 6: extern int t(void);
 7: int main(int argc, char **argv)
 8: {
 9:   if (argc > 1000000) {
10:     int (* volatile tp)(void)=(int (*)(void))&t;
11:     printf("%d", (*tp)());
12:   }
13: 
14:   return !!argv[argc];
15: }
16: int t(void) { void ((*volatile p)()); p = (void ((*)()))crc32_combine; return !p; }
/* end */

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

have_func: checking for adler32_combine() in zlib.h... -------------------- yes

"gcc -o conftest -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC conftest.c  -L. -L../.. -L. -fstack-protector-strong -rdynamic -Wl,-export-dynamic    -lz  -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  -lz  -lm   -lc"
checked program was:
/* begin */
 1: #include "ruby.h"
 2: 
 3: #include <zlib.h>
 4: 
 5: /*top*/
 6: extern int t(void);
 7: int main(int argc, char **argv)
 8: {
 9:   if (argc > 1000000) {
10:     int (* volatile tp)(void)=(int (*)(void))&t;
11:     printf("%d", (*tp)());
12:   }
13: 
14:   return !!argv[argc];
15: }
16: int t(void) { void ((*volatile p)()); p = (void ((*)()))adler32_combine; return !p; }
/* end */

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

have_type: checking for z_crc_t in zlib.h... -------------------- yes

"gcc -I../../.ext/include/x86_64-linux -I../.././include -I../.././ext/zlib    -g -O2 -fPIC   -c conftest.c"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <zlib.h>
4: 
5: /*top*/
6: typedef z_crc_t conftest_type;
7: int conftestval[sizeof(conftest_type)?1:-1];
/* end */

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

extconf.h is:
/* begin */
1: #ifndef EXTCONF_H
2: #define EXTCONF_H
3: #define HAVE_ZLIB_H 1
4: #define HAVE_CRC32_COMBINE 1
5: #define HAVE_ADLER32_COMBINE 1
6: #define HAVE_TYPE_Z_CRC_T 1
7: #endif
/* end */