util: add detection of openpty function

All UNIX platforms we care about have openpty() in the libutil
library. Use of pty.h must also be made conditional, excluding
Win32.
Reviewed-by: NPavel Hrdina <phrdina@redhat.com>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>

build-aux/syntax-check.mk

@@ -2342,3 +2342,6 @@ exclude_file_name_regexp--sc_prohibit_strcmp = \
 
 exclude_file_name_regexp--sc_prohibit_backslash_alignment = \
   ^build-aux/syntax-check\.mk$$
+
+exclude_file_name_regexp--sc_prohibit_always_true_header_tests = \
+  ^src/util/virfile\.c$$

configure.ac

@@ -383,10 +383,13 @@ dnl Availability of various common headers (non-fatal if missing).
 AC_CHECK_HEADERS([\
   ifaddrs.h \
   libtasn1.h \
+  util.h \
+  libutil.h \
   linux/magic.h \
   mntent.h \
   net/ethernet.h \
   netinet/tcp.h \
+  pty.h \
   pwd.h \
   stdarg.h \
   syslog.h \
@@ -430,6 +433,7 @@ dnl header could be found.
 AM_CONDITIONAL([HAVE_LIBTASN1], [test "x$ac_cv_header_libtasn1_h" = "xyes"])
 
 AC_CHECK_LIB([intl],[gettext],[])
+AC_CHECK_LIB([util],[openpty],[])
 
 
 dnl

src/util/Makefile.inc.am

@@ -282,6 +282,7 @@ libvirt_util_la_CFLAGS = \
 	$(NULL)
 libvirt_util_la_LIBADD = \
 	-lm \
+	$(OPENPTY_LIBS) \
 	$(CAPNG_LIBS) \
 	$(YAJL_LIBS) \
 	$(LIBNL_LIBS) \

src/util/virfile.c

@@ -27,7 +27,19 @@
 
 #include <passfd.h>
 #include <fcntl.h>
-#include <pty.h>
+#include <termios.h>
+#ifdef HAVE_PTY_H
+/* Linux openpty */
+# include <pty.h>
+#endif /* !HAVE_PTY_H */
+#ifdef HAVE_UTIL_H
+/* macOS openpty */
+# include <util.h>
+#endif /* !HAVE_LIBUTIL_H */
+#ifdef HAVE_LIBUTIL_H
+/* FreeBSD openpty */
+# include <libutil.h>
+#endif /* !HAVE_LIBUTIL_H */
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/socket.h>