CFLAGS="-Wall -Wextra -Wconversion $CFLAGS"
fi
-AC_CHECK_HEADERS([fcntl.h error.h])
+AC_CHECK_HEADERS([error.h])
+AC_CHECK_HEADERS([fcntl.h],
+ [],[AC_MSG_ERROR([header is required])])
AC_TYPE_PID_T
AC_TYPE_SIZE_T
AC_FUNC_FORK
AC_CHECK_FUNCS([memmove setenv],
[],[AC_MSG_ERROR([function is required])])
+AC_CHECK_FUNCS([execvpe])
dnl Thanks to gperftools' configure.ac (https://code.google.com/p/gperftools).
AC_MSG_CHECKING([for __builtin_expect])