android: add script in Android archive to create a SDK

Also,
- Move mingw's pkg-support into build-scripts
- Add type annotations to python scripts for mypy
- ci: use v4 tag of actions/cache
- cmake: use PYTHON3_EXECUTABLE for running xxd.py
  (Python3::Interpreter is not always recognized.)

build-scripts/pkg-support/mingw/INSTALL.txt

@@ -0,0 +1,25 @@
+
+The 32-bit files are in i686-w64-mingw32
+The 64-bit files are in x86_64-w64-mingw32
+
+To install SDL for 32-bit x86 executables (i686):
+    make install-i686
+
+To install SDL for 64-bit x86 executables (x86_64):
+    make install-x86_64
+
+To install both:
+    make install-all
+
+Use DESTDIR to change the target location
+    mkdir $HOME/mingw32-prefix
+    make install-i686 DESTDIR=$HOME/mingw32-prefix
+
+Look at the example programs in ./test, and check out online documentation:
+    https://wiki.libsdl.org/SDL3/FrontPage
+
+Join the SDL discourse server if you want to join the community:
+    https://discourse.libsdl.org/
+
+That's it!
+Sam Lantinga <slouken@libsdl.org>

build-scripts/pkg-support/mingw/Makefile

@@ -0,0 +1,37 @@
+#
+# Makefile for installing the mingw32 version of the SDL library
+
+DESTDIR = /usr/local
+ARCHITECTURES := i686-w64-mingw32 x86_64-w64-mingw32
+
+default:
+	@echo "Run \"make install-i686\" to install 32-bit"
+	@echo "Run \"make install-x86_64\" to install 64-bit"
+	@echo "Run \"make install-all\" to install both"
+	@echo "Add DESTDIR=/custom/path to change the destination folder"
+
+install:
+	@if test -d $(ARCH) && test -d $(DESTDIR); then \
+		(cd $(ARCH) && cp -rv bin include lib share $(DESTDIR)/); \
+	else \
+		echo "*** ERROR: $(ARCH) or $(DESTDIR) does not exist!"; \
+		exit 1; \
+	fi
+
+install-i686:
+	$(MAKE) install ARCH=i686-w64-mingw32
+
+install-x86_64:
+	$(MAKE) install ARCH=x86_64-w64-mingw32
+
+install-all:
+	@if test -d $(DESTDIR); then \
+		for arch in $(ARCHITECTURES); do \
+			$(MAKE) install ARCH=$$arch DESTDIR=$(DESTDIR)/$$arch; \
+		done \
+	else \
+		echo "*** ERROR: $(DESTDIR) does not exist!"; \
+		exit 1; \
+	fi
+
+.PHONY: default install install-i686 install-x86_64 install-all

build-scripts/pkg-support/mingw/cmake/SDL3Config.cmake

@@ -0,0 +1,19 @@
+# SDL3 CMake configuration file:
+# This file is meant to be placed in a cmake subfolder of SDL3-devel-3.x.y-mingw
+
+if(CMAKE_SIZEOF_VOID_P EQUAL 4)
+    set(sdl3_config_path "${CMAKE_CURRENT_LIST_DIR}/../i686-w64-mingw32/lib/cmake/SDL3/SDL3Config.cmake")
+elseif(CMAKE_SIZEOF_VOID_P EQUAL 8)
+    set(sdl3_config_path "${CMAKE_CURRENT_LIST_DIR}/../x86_64-w64-mingw32/lib/cmake/SDL3/SDL3Config.cmake")
+else()
+    set(SDL3_FOUND FALSE)
+    return()
+endif()
+
+if(NOT EXISTS "${sdl3_config_path}")
+    message(WARNING "${sdl3_config_path} does not exist: MinGW development package is corrupted")
+    set(SDL3_FOUND FALSE)
+    return()
+endif()
+
+include("${sdl3_config_path}")

build-scripts/pkg-support/mingw/cmake/SDL3ConfigVersion.cmake

@@ -0,0 +1,19 @@
+# SDL3 CMake version configuration file:
+# This file is meant to be placed in a cmake subfolder of SDL3-devel-3.x.y-mingw
+
+if(CMAKE_SIZEOF_VOID_P EQUAL 4)
+    set(sdl3_config_path "${CMAKE_CURRENT_LIST_DIR}/../i686-w64-mingw32/lib/cmake/SDL3/SDL3ConfigVersion.cmake")
+elseif(CMAKE_SIZEOF_VOID_P EQUAL 8)
+    set(sdl3_config_path "${CMAKE_CURRENT_LIST_DIR}/../x86_64-w64-mingw32/lib/cmake/SDL3/SDL3ConfigVersion.cmake")
+else()
+    set(PACKAGE_VERSION_UNSUITABLE TRUE)
+    return()
+endif()
+
+if(NOT EXISTS "${sdl3_config_path}")
+    message(WARNING "${sdl3_config_path} does not exist: MinGW development package is corrupted")
+    set(PACKAGE_VERSION_UNSUITABLE TRUE)
+    return()
+endif()
+
+include("${sdl3_config_path}")