Zlib and Bz2 link targets hard coded

When using static compiled libs for zlib and bz2 - I can specify the target name when calling b2 as follows:

`-s ZLIB_BINARY=zlibstatic -s BZIP2_BINARY=bz2_static`

However, these target names never make it into the resulting generated cmake file:
This was generated in libboost_iostreams-variant-vc143-mt-gd-x64-1_86-static.cmake:
```
if(CMAKE_CONFIGURATION_TYPES)
set_property(TARGET Boost::iostreams APPEND PROPERTY INTERFACE_LINK_LIBRARIES
"$<$:bz2;z>")
else()
set_property(TARGET Boost::iostreams APPEND PROPERTY INTERFACE_LINK_LIBRARIES
bz2 z)
endif()
```

I see there is a merged PR that addesses this: https://github.com/boostorg/iostreams/pull/176

However this is really a bug since the name being provided to b2 isn't making it down to the generated cmake configuration files.

Start by reviewing the merged PR linked in the issue and the generated libboost_iostreams-variant-vc143-mt-gd-x64-1_86-static.cmake example. Check how the b2 settings ZLIB_BINARY and BZIP2_BINARY are represented in the generated CMake link targets; the issue is addressed when the configured names appear there instead of bz2 and z.

Written by the indexing model from the issue text.