How to cross-compile boost for QNX 7.0

# For QNX OS, use the following commands:

```

./bootstrap.sh --prefix=~/install --without-icu \

    --with-libraries=atomic,filesystem,serialization,graph,graph_parallel,iostreams,log,math,system,thread,date_time,regex,timer,chrono,program_options

# For QNX x86_64:

./b2 toolset=qcc target-os=qnxnto link=static cxxflags=-fPIC cflags=-fPIC \

--disable-icu -s NO_BZIP2=1 -j32 install

# For QNX aarch64:

./b2 toolset=qcc target-os=qnxnto link=static --disable-icu  \

cxxflags="-Vgcc_ntoaarch64le -Y_gpp -Wc,-std=gnu++0x -D_LITTLE_ENDIAN" \

linkflags="-Vgcc_ntoaarch64le -Y_gpp -lang-c++" -j32 install

# To clean up built binaries

./b2 --clean-all -n

```