configure: define HAVE_PIPE2 if we have pipe2() and O_CLOEXEC.

This commit adds a new run for pipe2() and O_CLOEXEC. If a program
can be executed, define HAVE_PIPE2.

Signed-off-by: Tom Li <tomli@tomli.me>

configure

@@ -152,6 +152,9 @@ issolaris() {
 check_compile 'whether we have GNU-style getservbyname_r()' "-DHAVE_GNU_GETSERVBYNAME_R" \
 '#define _GNU_SOURCE\n#include <netdb.h>\nint main() {\nstruct servent *se = 0;struct servent se_buf;char buf[1024];\ngetservbyname_r("foo", (void*) 0, &se_buf, buf, sizeof(buf), &se);\nreturn 0;}'
 
+check_compile 'whether we have pipe2() and O_CLOEXEC' "-DHAVE_PIPE2" \
+'#define _GNU_SOURCE\n#include <fcntl.h>\n#include <unistd.h>\nint main() {\nint pipefd[2];\npipe2(pipefd, O_CLOEXEC);\nreturn 0;}'
+
 check_define __APPLE__ && {
 	mac_detected=true
 	check_define __x86_64__ && mac_64=true