Move earcut to deps_src

deps_src/earcut/CMakeLists.txt

@@ -0,0 +1,13 @@
+cmake_minimum_required(VERSION 3.13)
+project(earcut)
+
+add_library(earcut INTERFACE)
+
+target_include_directories(earcut SYSTEM
+    INTERFACE
+        ${CMAKE_CURRENT_SOURCE_DIR}
+)
+
+target_sources(earcut INTERFACE
+    ${CMAKE_CURRENT_SOURCE_DIR}/earcut.hpp
+)