Zlib and Bz2 link targets hard coded

[jammerxd]

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
    "$<$<CONFIG:debug>: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: #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.