cups: Fix build for Linux (#19709)
cups: Fix build for Linux (#19709)

The error was:

```
==> ./configure --with-components=core --without-bundledir --prefix=/home/linuxbrew/.linuxbrew/Cellar/cups/2.3.1
==> make install
Last 15 lines from /home/linuxbrew/.cache/Homebrew/Logs/cups/02.make:
make[1]: *** [../Makedefs:270: dest.o] Error 1
In file included from cups-private.h:21:0,
                 from dest-job.c:13:
http-private.h:263:3: error: unknown type name 'gss_OID'
   gss_OID   gssmech; /* Authentication mechanism */
   ^
http-private.h:264:3: error: unknown type name 'gss_ctx_id_t'
   gss_ctx_id_t  gssctx;  /* Authentication context */
   ^
http-private.h:265:3: error: unknown type name 'gss_name_t'
   gss_name_t  gssname; /* Authentication server name */
   ^
make[1]: *** [../Makedefs:270: dest-job.o] Error 1
make[1]: Leaving directory '/tmp/cups-20200225-5715-1jzt133/cups-2.3.1/cups'
make: *** [Makefile:167: install-data] Error 2
```

The fix comes from [this StackOverflow answer](https://stackoverflow.com/a/19584147).

Fixes #19707.

Signed-off-by: Issy Long <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@issyl0.co.uk>
rwhogg/homebrew-core,maxim-belkin/homebrew-core,rwhogg/homebrew-core,maxim-belkin/homebrew-core,Linuxbrew/homebrew-core,Linuxbrew/homebrew-core