#3 special flags for AIX compiler

[lord]

"icmpmonitor has been succesfully compiled and executed on a
RS/6000 PowerPC. The OS is AIX 4.3.2 and the compiler is C for AIX compiler 4.3.0.0.
In the Makefile created by configure, add -qcpluscmt in CFLAGS."

Reported by: Damien Jeandel

I think some configure.in tweaking required to
do this.