dependencies: allow to fallback on CMake to find the SDL2 library

On Windows, the SDL2 library is generally provided with only CMake config
files. This commit allows meson to fallback on CMake as a last resort to
find the SDL2 library.

docs/markdown/Dependencies.md

@@ -728,10 +728,10 @@ your own risk.
 ## SDL2
 
 SDL2 can be located using `pkg-confg`, the `sdl2-config` config tool,
-or as an OSX framework.
+as an OSX framework, or `cmake`.
 
-`method` may be `auto`, `config-tool`, `extraframework` or
-`pkg-config`.
+`method` may be `auto`, `config-tool`, `extraframework`,
+`pkg-config` or `cmake`.
 
 ## Shaderc
 

mesonbuild/dependencies/ui.py

@@ -252,8 +252,9 @@ gl_factory = DependencyFactory(
 
 sdl2_factory = DependencyFactory(
     'sdl2',
-    [DependencyMethods.PKGCONFIG, DependencyMethods.CONFIG_TOOL, DependencyMethods.EXTRAFRAMEWORK],
+    [DependencyMethods.PKGCONFIG, DependencyMethods.CONFIG_TOOL, DependencyMethods.EXTRAFRAMEWORK, DependencyMethods.CMAKE],
     configtool_class=SDL2DependencyConfigTool,
+    cmake_name='SDL2',
 )
 
 vulkan_factory = DependencyFactory(

test cases/frameworks/16 sdl2/meson_options.txt

@@ -1,6 +1,6 @@
 option(
     'method',
     type : 'combo',
-    choices : ['auto', 'pkg-config', 'config-tool', 'sdlconfig', 'extraframework'],
+    choices : ['auto', 'pkg-config', 'config-tool', 'sdlconfig', 'extraframework', 'cmake'],
     value : 'auto',
 )

test cases/frameworks/16 sdl2/test.json

@@ -6,7 +6,8 @@
         { "val": "pkg-config" },
         { "val": "config-tool" },
         { "val": "sdlconfig" },
-        { "val": "extraframework", "skip_on_os": ["!darwin"], "skip_on_jobname": ["macos"] }
+        { "val": "extraframework", "skip_on_os": ["!darwin"], "skip_on_jobname": ["macos"] },
+        { "val": "cmake", "skip_on_jobname": ["bionic"] }
       ]
     }
   },