"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.1.0 -I/usr/include/ruby-2.1.0/ruby/backward -I/usr/include/ruby-2.1.0 -I. -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-z,relro -L/home/pere/src/debian/ruby/ruby2.1/debian/lib -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.1  -lpthread -lgmp -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/usr/include/x86_64-linux-gnu/ruby-2.1.0 -I/usr/include/ruby-2.1.0/ruby/backward -I/usr/include/ruby-2.1.0 -I. -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC    -Werror -c conftest.c"
checked program was:
/* begin */
1: #include "ruby.h"
2:
3: int main() {return 0;}
/* end */

have_library: checking for gzdopen() in -lz... -------------------- no

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.1.0 -I/usr/include/ruby-2.1.0/ruby/backward -I/usr/include/ruby-2.1.0 -I. -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  -g -DXP_UNIX -Wall -Wcast-qual -Wwrite-strings -Wconversion -Wmissing-noreturn -Winline conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-z,relro -L/home/pere/src/debian/ruby/ruby2.1/debian/lib -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.1 -lz  -lpthread -lgmp -ldl -lcrypt -lm   -lc "
conftest.c:3:18: fatal error: zlib.h: No such file or directory
 #include <zlib.h>
                  ^
compilation terminated.
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:     printf("%p", &t);
11:   }
12:
13:   return 0;
14: }
15: int t(void) { void ((*volatile p)()); p = (void ((*)()))gzdopen; return 0; }
/* end */

"gcc -o conftest -I/usr/include/x86_64-linux-gnu/ruby-2.1.0 -I/usr/include/ruby-2.1.0/ruby/backward -I/usr/include/ruby-2.1.0 -I. -D_FORTIFY_SOURCE=2   -g -O2 -fstack-protector-strong -Wformat -Werror=format-security -fPIC  -g -DXP_UNIX -Wall -Wcast-qual -Wwrite-strings -Wconversion -Wmissing-noreturn -Winline conftest.c  -L. -L/usr/lib/x86_64-linux-gnu -L. -Wl,-z,relro -L/home/pere/src/debian/ruby/ruby2.1/debian/lib -fstack-protector -rdynamic -Wl,-export-dynamic     -lruby-2.1 -lz  -lpthread -lgmp -ldl -lcrypt -lm   -lc "
conftest.c:3:18: fatal error: zlib.h: No such file or directory
 #include <zlib.h>
                  ^
compilation terminated.
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:     printf("%p", &t);
11:   }
12:
13:   return 0;
14: }
15: int t(void) { gzdopen(); return 0; }
/* end */

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