Fixed a boost build issue when OPENVDB_USE_DELAYED_LOADING is set to OFF

Signed-off-by: Nick Avramoussis <4256455+Idclip@users.noreply.github.com>

Author: Idclip

doc/dependencies.txt

@@ -37,7 +37,7 @@ Reference Platform, but for those that do, their specified versions are
 
 Component               | Requirements                                      | Optional
 ----------------------- | ------------------------------------------------- | --------
-OpenVDB Core Library    | CMake, C++17 compiler, TBB::tbb                   | Blosc, ZLib, Log4cplus, IlmBase::Half, Boost::iostream
+OpenVDB Core Library    | CMake, C++17 compiler, TBB::tbb, Boost::headers   | Blosc, ZLib, Log4cplus, IlmBase::Half, Boost::iostream
 OpenVDB Print           | Core Library dependencies                         | -
 OpenVDB LOD             | Core Library dependencies                         | -
 OpenVDB Render          | Core Library dependencies                         | OpenEXR, IlmBase, libpng
@@ -66,7 +66,7 @@ IlmBase        | 2.4     | 3.1         | Used half precision floating points and
 OpenEXR        | 2.4     | 3.1         | EXR serialization support                                         | Y       | Y        | http://www.openexr.com
 TBB            | 2020.2  | 2020.3      | Threading Building Blocks - template library for task parallelism | Y       | Y        | https://www.threadingbuildingblocks.org
 ZLIB           | 1.2.7   | Latest      | Compression library for disk serialization compression            | Y       | Y        | https://www.zlib.net
-Boost          | 1.73    | 1.76        | Components: iostreams, python, numpy                              | Y       | Y        | https://www.boost.org
+Boost          | 1.73    | 1.76        | Components: headers, iostreams, python, numpy                     | Y       | Y        | https://www.boost.org
 LLVM           | 10.0.0  | 10.0.0*     | Target-independent code generation                                | Y       | Y        | https://llvm.org/
 Bison          | 3.0.0   | 3.7.0       | General-purpose parser generator                                  | Y       | Y        | https://www.gnu.org/software/gcc
 Flex           | 2.6.0   | 2.6.4       | Fast lexical analyzer generator                                   | Y       | Y        | https://github.com/westes/flex

openvdb/openvdb/CMakeLists.txt

@@ -119,6 +119,8 @@ endif()
 
 if(OPENVDB_USE_DELAYED_LOADING)
   find_package(Boost ${MINIMUM_BOOST_VERSION} REQUIRED COMPONENTS iostreams)
+else()
+  find_package(Boost ${MINIMUM_BOOST_VERSION} REQUIRED COMPONENTS headers)
 endif()
 
 if(OPENVDB_FUTURE_DEPRECATION AND FUTURE_MINIMUM_BOOST_VERSION)
@@ -255,6 +257,8 @@ endif()
 
 if(OPENVDB_USE_DELAYED_LOADING)
   list(APPEND OPENVDB_CORE_DEPENDENT_LIBS Boost::iostreams)
+else()
+  list(APPEND OPENVDB_CORE_DEPENDENT_LIBS Boost::headers)
 endif()
 
 if(WIN32)

pendingchanges/boost_build_fix.txt

@@ -0,0 +1,3 @@
+Build:
+    - Fixed a build issue where Boost was not being pulled in when 
+    OPENVDB_USE_DELAYED_LOADING was set to OFF.