I forgot to search Google groups! Here's the answer that I found there, and
which worked for me as well:

"From: Bernhard R. Erdmann (be AT berdmann DOT de)
Subject: Re: Error compiling on AIX 4.3.3.0.09 
Newsgroups: list.amanda.users
View this article only 
Date: 2001-10-02 16:30:14 PST 
 

> I am trying to compile Amanda (2.4.2.p2) on an AIX 4.3.3 box to be used as
a
> client only (I used the --without-server configure option).  It dies
during
> the compile with this message: [...]
> getfsent.c: In function `open_fstab':
> getfsent.c:154: `MNTTAB' undeclared (first use in this function)
> getfsent.c:154: (Each undeclared identifier is reported only once
> getfsent.c:154: for each function it appears in.)
> make: 1254-004 The error code from the last command is 1.
[...]

A temporary solution is to kick away or to rename mntent.h to
mntent.h.ibmsucks. Don't forget to "make distclean" or "rm config.cache"
before another shot of "./configure --with-user=... ---with-group=...
--with-blabla=..."
Nobody has come up with a general solution for AIX 4.3.3, yet. Though is
has bitten many Amanda users/admins on AIX 4.3.3. :-("



-----Original Message-----
From: Dombrowski, Todd [mailto:Todd.Dombrowski AT FMR DOT COM]
Sent: Monday, September 30, 2002 12:17 PM
To: 'amanda-users AT amanda DOT org'
Subject: Error compiling AMANDA sources on AIX 4.3 (`MNTTAB' undeclared)

I recently ran across an issue on a new AIX 4.3 server we installed a few
weeks back. I just tried to compile amanda and I received the following
error (running `make`):

make[1]: Entering directory `/tmp/amanda-install/amanda-2.4.2p2/client-src'
/usr/bin/sh ../libtool --mode=compile gcc -DHAVE_CONFIG_H -I. -I.
-I../config -I../common-src    -g -O2   -c amandates.c
gcc -DHAVE_CONFIG_H -I. -I. -I../config -I../common-src -g -O2 -c
amandates.c -o amandates.o
echo timestamp > amandates.lo
/usr/bin/sh ../libtool --mode=compile gcc -DHAVE_CONFIG_H -I. -I.
-I../config -I../common-src    -g -O2   -c getfsent.c
gcc -DHAVE_CONFIG_H -I. -I. -I../config -I../common-src -g -O2 -c getfsent.c
-o getfsent.o
getfsent.c: In function `open_fstab':
getfsent.c:154: `MNTTAB' undeclared (first use in this function)
getfsent.c:154: (Each undeclared identifier is reported only once
getfsent.c:154: for each function it appears in.)
make[1]: *** [getfsent.lo] Error 1
make[1]: Leaving directory `/tmp/amanda-install/amanda-2.4.2p2/client-src'
make: *** [all-recursive] Error 1