have_header: checking for sys/cdefs.h... -------------------- yes

"gcc -E -I../../../.ext/include/x86_64-linux -I../../.././include -I../../.././ext/digest/rmd160    -O3 -ggdb3 -Wall -Wextra -Wdeprecated-declarations -Wduplicated-cond -Wimplicit-function-declaration -Wimplicit-int -Wmisleading-indentation -Wpointer-arith -Wwrite-strings -Wimplicit-fallthrough=0 -Wmissing-noreturn -Wno-cast-function-type -Wno-constant-logical-operand -Wno-long-long -Wno-missing-field-initializers -Wno-overlength-strings -Wno-packed-bitfield-compat -Wno-parentheses-equality -Wno-self-assign -Wno-tautological-compare -Wno-unused-parameter -Wno-unused-value -Wsuggest-attribute=format -Wsuggest-attribute=noreturn -Wunused-variable  -fPIC  conftest.c -o conftest.i"
checked program was:
/* begin */
1: #include "ruby.h"
2: 
3: #include <sys/cdefs.h>
/* end */

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

extconf.h is:
/* begin */
1: #ifndef EXTCONF_H
2: #define EXTCONF_H
3: #define NDEBUG 1
4: #define HAVE_CONFIG_H 1
5: #define HAVE_SYS_CDEFS_H 1
6: #endif
/* end */