add lodepng as an external, have video_core depend on it

externals/CMakeLists.txt

@@ -100,3 +100,6 @@ if (ENABLE_WEB_SERVICE)
     add_library(cpp-jwt INTERFACE)
     target_include_directories(cpp-jwt INTERFACE ./cpp-jwt/include)
 endif()
+
+# lodepng
+add_subdirectory(lodepng)

externals/lodepng/CMakeLists.txt

@@ -0,0 +1,7 @@
+add_library(lodepng
+    lodepng.cpp
+    lodepng.h
+)
+
+create_target_directory_groups(lodepng)
+target_include_directories(lodepng INTERFACE .)

externals/lodepng/LICENSE

@@ -0,0 +1,21 @@
+Copyright (c) 2005-2018 Lode Vandevenne
+
+This software is provided 'as-is', without any express or implied
+warranty. In no event will the authors be held liable for any damages
+arising from the use of this software.
+
+Permission is granted to anyone to use this software for any purpose,
+including commercial applications, and to alter it and redistribute it
+freely, subject to the following restrictions:
+
+    1. The origin of this software must not be misrepresented; you must not
+    claim that you wrote the original software. If you use this software
+    in a product, an acknowledgment in the product documentation would be
+    appreciated but is not required.
+
+    2. Altered source versions must be plainly marked as such, and must not be
+    misrepresented as being the original software.
+
+    3. This notice may not be removed or altered from any source
+    distribution.
+    

src/video_core/CMakeLists.txt

@@ -92,7 +92,7 @@ endif()
 create_target_directory_groups(video_core)
 
 target_link_libraries(video_core PUBLIC common core)
-target_link_libraries(video_core PRIVATE glad nihstro-headers)
+target_link_libraries(video_core PRIVATE glad nihstro-headers lodepng)
 
 if (ARCHITECTURE_x86_64)
     target_link_libraries(video_core PUBLIC xbyak)