The warnings that I see are:
gcc -DHAVE_CONFIG_H -I. -I. -I. -I/usr/local/lib/include -Wall
-Wstrict-prototypes -g -O2 -c auth_ldap.c
auth_ldap.c:356:9: warning: pasting "." and "mailbox" does not give a
valid preprocessing token
auth_ldap.c:356:9: warning: pasting "." and "mailbox" does not give a
valid preprocessing token
auth_ldap.c:357:9: warning: pasting "." and "mboxtype" does not give a
valid preprocessing token
auth_ldap.c:357:9: warning: pasting "." and "mboxtype" does not give a
valid preprocessing token
auth_ldap.c:358:9: warning: pasting "." and "user" does not give a valid
preprocessing token
auth_ldap.c:358:9: warning: pasting "." and "user" does not give a valid
preprocessing token
auth_ldap.c:359:9: warning: pasting "." and "group" does not give a
valid preprocessing token
auth_ldap.c:359:9: warning: pasting "." and "group" does not give a
valid preprocessing token
...
gcc -DHAVE_CONFIG_H -I. -I. -I. -I/usr/local/lib/include -Wall
-Wstrict-prototypes -g -O2 -c maildir.c
maildir.c:103:2: warning: #warning IGNORE_CCLIENT_METADATA not supported
with maildir.
maildir.c: In function `maildir_send_message':
maildir.c:177: warning: implicit declaration of function `open'