compilation error: getopt.h not found on AIX

Hi, I tried to compile it on AIX 7.2 but failed with error during make:

```
CC src/google-authenticator.o
src/google-authenticator.c:25:10: fatal error: getopt.h: No such file or directory
#include
^~~~~~~~~~
compilation terminated.
make: 1254-004 The error code from the last command is 1.
```

I tried to add getopt module but not sure if the steps are correct:

```
./bootstrap.sh
/usr/local/src/gnulib/gnulib-tool --import getopt
/usr/local/src/gnulib/gnulib-tool --add-import getopt
/usr/local/src/gnulib/gnulib-tool --add-import vasprintf
./configure
make
```
Can only found lib/getopt.in.h but nowhere else.

Would anyone please help? Sorry for the newbie question.

Thanks and rgds