FindBoost: Add check headers for `zlib` and `bzip2`

The official Windows builds of Boost have internal implementations for
`zlib` and `bzip2` libraries used by Boost::iostreams library, e.g.

* boost_bzip2-vc140-mt-1_59.lib
* boost_zlib-vc140-mt-1_59.lib

Add check headers for these so that users can specify them as
components without any warnings.

Reviewed-by: Roger Leigh <[email protected]>

Modules/FindBoost.cmake

@@ -808,6 +808,10 @@ function(_Boost_COMPONENT_HEADERS component _hdrs)
   set(_Boost_UNIT_TEST_FRAMEWORK_HEADERS "boost/test/framework.hpp")
   set(_Boost_WAVE_HEADERS                "boost/wave.hpp")
   set(_Boost_WSERIALIZATION_HEADERS      "boost/archive/text_wiarchive.hpp")
+  if(WIN32)
+    set(_Boost_BZIP2_HEADERS             "boost/iostreams/filter/bzip2.hpp")
+    set(_Boost_ZLIB_HEADERS              "boost/iostreams/filter/zlib.hpp")
+  endif()
 
   string(TOUPPER ${component} uppercomponent)
   set(${_hdrs} ${_Boost_${uppercomponent}_HEADERS} PARENT_SCOPE)