Upgrade to SDL2.0.20 (#270)

* Upgrade to SDL2.0.20

Signed-off-by: Patrick Roncagliolo <ronca.pat@gmail.com>

sdl2_vendor/CMakeLists.txt

@@ -14,10 +14,10 @@ endif()
 
 if(NOT SDL2_FOUND)
   include(ExternalProject)
-  ExternalProject_Add(SDL2-2.0.14
-    PREFIX SDL2-2.0.12
-    URL https://www.libsdl.org/release/SDL2-2.0.14.tar.gz
-    URL_MD5 76ed4e6da9c07bd168b2acd9bfefab1b
+  ExternalProject_Add(SDL2-2.0.20
+    PREFIX SDL2-2.0.20
+    URL https://www.libsdl.org/release/SDL2-2.0.20.tar.gz
+    URL_MD5 a53acc02e1cca98c4123229069b67c9e
     CMAKE_ARGS
       -DBUILD_SHARED_LIBS=ON
       -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}

sdl2_vendor/sdl2-windows-add-vcruntime.patch

@@ -1,13 +1,10 @@
---- a/CMakeLists.txt.orig	2020-04-01 14:23:24.000000000 +0000
-+++ b/CMakeLists.txt	2020-04-01 14:23:38.000000000 +0000
-@@ -1556,9 +1556,9 @@ elseif(WINDOWS)
+--- a/CMakeLists.txt.orig
++++ b/CMakeLists.txt
+@@ -1693,6 +1693,6 @@ elseif(WINDOWS)
    endif()
 
    # Libraries for Win32 native and MinGW
    if(NOT WINDOWS_STORE)
 -    list(APPEND EXTRA_LIBS user32 gdi32 winmm imm32 ole32 oleaut32 version uuid advapi32 setupapi shell32)
 +    list(APPEND EXTRA_LIBS vcruntime user32 gdi32 winmm imm32 ole32 oleaut32 version uuid advapi32 setupapi shell32)
    endif()
-
-   # TODO: in configure.ac the check for timers is set on
-   # cygwin | mingw32* - does this include mingw32CE?