Update find_package for msgpack to work with 5.x and 6.x.

Adapted from: https://github.com/msgpack/msgpack-c/wiki/Q%26A#how-to-support-both-msgpack-c-c-version-5x-and-6x-

Note that 6.x also defines compile definitions that must be respected.

tensilelite/Tensile/Source/lib/CMakeLists.txt

@@ -96,22 +96,31 @@ if(TENSILE_USE_LLVM OR TENSILE_USE_MSGPACK)
 endif()
 
 if(TENSILE_USE_MSGPACK)
-    find_package(msgpack REQUIRED)
-    target_compile_definitions(TensileHost PUBLIC -DTENSILE_MSGPACK=1)
-
-    if(TARGET msgpackc-cxx)
-        get_target_property(msgpack_inc msgpackc-cxx INTERFACE_INCLUDE_DIRECTORIES)
-    elseif(TARGET msgpackc)
-        get_target_property(msgpack_inc msgpackc INTERFACE_INCLUDE_DIRECTORIES)
-    endif()
-
-    if(DEFINED msgpack_inc)
-        # include C++ headers manually
-        # External header includes included as system files
+    # See: https://github.com/msgpack/msgpack-c/wiki/Q%26A#how-to-support-both-msgpack-c-c-version-5x-and-6x-
+    # Prefer 6.x (msgpack-cxx) as that is what we bundle in the build.
+    find_package(msgpack-cxx CONFIG)
+    if(msgpack-cxx_FOUND)
+        # Version 6.x
+        get_target_property(msgpack_inc msgpack-cxx INTERFACE_INCLUDE_DIRECTORIES)
+        get_target_property(msgpack_defs msgpack-cxx INTERFACE_COMPILE_DEFINITIONS)
         target_include_directories(TensileHost
             SYSTEM PRIVATE $<BUILD_INTERFACE:${msgpack_inc}>
         )
+        target_compile_definitions(TensileHost PRIVATE $<BUILD_INTERFACE:${msgpack_defs}>)
+        message(STATUS "Found msgpack-cxx (>=6.x): ${msgpack_inc} ${msgpack_defs}")
+    else()
+        # Fallback to <= 5.x
+        find_package(msgpackc-cxx CONFIG REQUIRED NAMES msgpackc-cxx msgpack)
+        get_target_property(msgpack_inc msgpackc INTERFACE_INCLUDE_DIRECTORIES)
+        get_target_property(msgpack_defs msgpackc INTERFACE_COMPILE_DEFINITIONS)
+        message(STATUS "Found msgpack (<=5.x): ${msgpack_inc} ${msgpack_defs}")
     endif()
+    target_include_directories(TensileHost
+        SYSTEM PRIVATE $<BUILD_INTERFACE:${msgpack_inc}>
+    )
+    target_compile_definitions(TensileHost PRIVATE $<BUILD_INTERFACE:${msgpack_defs}>)
+
+    target_compile_definitions(TensileHost PUBLIC -DTENSILE_MSGPACK=1)
 endif()
 
 if(TENSILE_USE_LLVM)