i guess you have already found the way to build boost for qnx..

assuming that you use Linux host and GNU c++ runtime,

1. build bjam

./bootstrap.sh ...other options...

2. build boost

./b2 toolset=qcc cxxflags=-Vgcc_ntox86_gpp target-os=qnx ...other options...

I'm a little late to the discussion but I thought I'd contribute in case it can help others.

I can cross-compile most of Boost 1.55 for Arm from Windows using the following command line:
.\b2 toolset=qcc target-os=qnxnto threadapi=pthread link=static -l240 --layout=system --without-python cxxflags="-
Vgcc_ntoarmv7le -Y_gpp -Wc,-std=gnu++0x -D_LITTLE_ENDIAN" linkflags="-Vgcc_ntoarmv7le -Y_gpp -lang-c++" -j7 > buildlog.
txt 2>&1

This should work on Linux and QNX as well. -j7 uses seven threads for compilation.

There will be several megabytes of compiler errors.

Remove -Wc,-std=gnu++0x if you don't want C++0x mode.

Replace -Vgcc_ntoarmv7le with -Vgcc_ntox86 to compile for x86.

A slightly better way to do it is to create a user-config.jam in your user directory and put the compiler options in it like this:
using qcc : arm : : <cxxflags>"-Vgcc_ntoarmv7le -Y_gpp -Wc,-std=gnu++0x -D_LITTLE_ENDIAN" <linkflags>"-Vgcc_ntoarmv7le -Y_gpp -lang-c+
+" ;

"arm" is just a name for the configuration.

The command line to use:
.\b2 toolset=qcc-arm target-os=qnxnto threadapi=pthread link=static -l240 --layout=system --without-python -j7 > 
buildlog.txt 2>&1