pty.c: Restore build on systems without cfmakeraw(3) (re: 5a2e7da)

The OpenSUSE patch uses cfmakeraw(3) which is on Linux, BSD and
macOS, but not portable. The build failed on Solaris and variants.

src/cmd/builtin/features/pty:
- Add simple test for the presence of cfmakeraw(3). I love iffe.

src/cmd/builtin/pty.c:
- Add POSIX compliant fallback flaggery for systems without it.

src/cmd/builtin/features/pty

@@ -11,6 +11,7 @@ header	stropts.h
 
 lib	openpty,_getpty,ptsname -lutil
 lib	grantpt,unlockpt,posix_openpt stdlib.h
+lib	cfmakeraw termios.h
 
 tst - output{
 	#include	<sys/types.h>

src/cmd/builtin/pty.c

@@ -236,7 +236,14 @@ mkpty(int* master, int* slave)
 	{
 		if (errno != ENOTTY)
 			error(-1, "unable to get standard error terminal attributes");
+#if _lib_cfmakeraw
 		cfmakeraw(&tty);
+#else
+		tty.c_iflag |= IGNPAR;
+		tty.c_iflag &= ~(ISTRIP | INLCR | IGNCR | ICRNL | IXON | IXANY | IXOFF);
+		tty.c_oflag &= ~OPOST;
+		tty.c_lflag &= ~(ISIG | ICANON | ECHO | ECHOE | ECHOK | ECHONL);
+#endif /* _lib_cfmakeraw */
 		ttyp = 0;
 	}
 	tty.c_lflag |= ICANON | IEXTEN | ISIG | ECHO|ECHOE|ECHOK|ECHOKE;