Ensure that system environment variable PATH includes the location of all the compilers mentioned above.

Download the source code of ICU version 3.6 for C from http://icu.sourceforge.net/download/3.6.html#ICU4C

At the shell prompt, execute the following commands:

gunzip -d < icu4c-3_6-src.tgz | tar -xf - 
cd icu/source/ 
chmod +x runConfigureICU configure install-sh
runConfigureICU AIX --disable-64bit-libs --disable-threads 
gmake
gmake check 
gmake install

Set the environment variable LIBPATH to point to the location of ICU. AIX uses the environment variable LIBPATH to search for dynamically linked libraries.