This is gdm 2.19.0:

In daemon/
In file included from filecheck.c:27:
filecheck.h:22: parse error before `uid_t'
filecheck.h:29: parse error before `uid_t'
filecheck.c:56: warning: no previous prototype for `gdm_file_check'
filecheck.c:175: warning: no previous prototype for `gdm_auth_file_check'

In gui/
In file included from gdmuser.c:34:
gdmuser.h:29: parse error before `uid_t'
gdmuser.h:29: warning: no semicolon at end of struct or union
gdmuser.h:34: parse error before `}'
gdmuser.c: In function `gdm_user_alloc':
gdmuser.c:58: sizeof applied to an incomplete type
gdmuser.c:60: dereferencing pointer to incomplete type
...

The following patch addresses these.