The AIX xlc 3.6.6 compiler does *NOT* like the INCLUDE_GLUE hackery on a #include.
The following test case demonstrates:
cd lwlib/
cat > z9.c << EOF
 #include "config.h"
 ATHENA_INCLUDE(foobar.h)
 #include ATHENA_INCLUDE(foobar.h)
EOF
xlc -E -I. -I/usr/local/include z9.c | tail 
 
 produces on stderr:
 "z9.c", line 3.11: 1506-341 (S) #include header must be ended before the end of
the line.
 "z9.c", line 3.10: 1506-234 (E) Expecting a new-line character on #include
directive.
 and on stdout:
 #line 11 "./../src/s/aix4.h"
 struct ether_addr;
 struct sockaddr_dl;
 #line 2 "z9.c"
 <X11/Xaw/foobar.h>
 #line 1 "/usr/local/include/X11"
R.>Q..>Sxpm.h>Tbpmplus.h 
 Seems to expand that X11 into the actual directory name.
 I'm surprised that #including a directory works, this is PROBABLY
 an IBM bug.
 /Valdis