Fix errors on Ubuntu with grantpt

[weierophinney]

I've had a few errors while compiling on Ubuntu. 18.04 (which has glibc 1.27).

First, I had to apply the patch defined in #2 to compile at all. Without both the -02 and SVR4 flags present, compilation failed.

With that patch applied, I then saw warnings similar to the following during compilation:

ttyrec.c: In function 'getslave':
ttyrec.c:447:2: warning: implicit declaration of function 'grantpt' [-Wimplicit-function-declaration]
  grantpt( master);
  ^~~~~~~

I would receive the same warnings for usager of each of unlockpt and ptsname. Compilation would finish, but any attempt to run ttyrec would result in the following error message:

open(fd, ORDWR): Bad address

I did some sleuthing, and it appears that the grantpt et al prototypes require additional macro definitions. What I found worked was the following:

#if defined(__linux__) || defined(__GLIBC__) || defined(__GNU__)
#define _GNU_SOURCE			/* GNU glibc grantpt() prototypes */
#endif

(Those lines MUST occur before #include <stdlib.h>.)

Once those lines were in place, along with the patch from #2, compilation worked.

(I received a few additional warnings, primarily around missing sentinels in execl calls and ignoring the return value of write, but these did not adversely affect the final binary produced.)

[AdamDanischewski]

Your changes worked for me, it looks like this project is abandoned. Maybe you can fork and improve it that way.