integrate Skate-specific rexglue SDK

.gitmodules

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+[submodule "third_party/rexglue-sdk"]
+	path = third_party/rexglue-sdk
+	url = https://github.com/mchughalex/rexglue-skate3.git
+	branch = skate3-sdk-clean
+

cmake/RexGlue.cmake

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+set(REXSDK_VERSION "" CACHE STRING "Override rexglue SDK package version")
+
+if(REXSDK_DIR AND EXISTS "${REXSDK_DIR}/CMakeLists.txt")
+    add_subdirectory("${REXSDK_DIR}" "${CMAKE_CURRENT_BINARY_DIR}/rexglue-sdk")
+    message(STATUS "Using rexglue SDK source tree: ${REXSDK_DIR}")
+else()
+    if(REXSDK_VERSION)
+        find_package(rexglue ${REXSDK_VERSION} EXACT QUIET CONFIG)
+    else()
+        find_package(rexglue 0.8.1.19 QUIET CONFIG)
+    endif()
+
+    if(NOT rexglue_FOUND)
+        message(FATAL_ERROR
+            "rexglue SDK not found. Set REXSDK_DIR to a rexglue-sdk source tree "
+            "or install the SDK package and set CMAKE_PREFIX_PATH.")
+    endif()
+
+    message(STATUS "Found rexglue SDK ${REXGLUE_VERSION_STRING} at ${rexglue_DIR}")
+endif()

third_party/rexglue-sdk

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+Subproject commit 9173ff4b017a178b6c2433bd925eb96d79dc764d