[sdl3] build error on x64-windows

Package: sdl3:x64-windows@3.4.4

**Host Environment**

- Host: x64-windows

- Compiler: MSVC 19.29.30159.0

- CMake Version: 4.3.1

- vcpkg-tool version: 2026-04-08-e0612b42ce44e55a0e630f2ee9d3c533a63d8bc1
vcpkg-scripts version: 0b88aacde4 2026-04-11 (4 days ago)

**To Reproduce**

`vcpkg install sdl3-mixer`

**Failure logs**

```
-- Using cached libsdl-org-SDL-release-3.4.4.tar.gz
-- Cleaning sources at D:/vcpkg/buildtrees/sdl3/src/ease-3.4.4-3ef55fe7e2.clean. Use --editable to skip cleaning for the packages you specify.
-- Extracting source D:/vcpkg/downloads/libsdl-org-SDL-release-3.4.4.tar.gz
-- Applying patch fix-freebsd.patch
-- Using source at D:/vcpkg/buildtrees/sdl3/src/ease-3.4.4-3ef55fe7e2.clean
CMake Error at ports/sdl3/portfile.cmake:48 (vcpkg_cmake_configure):
Unknown CMake command "vcpkg_cmake_configure".
Call Stack (most recent call first):
scripts/ports.cmake:206 (include)

```

Start with ports/sdl3/portfile.cmake at line 48 and the vcpkg install sdl3-mixer reproduction. Read scripts/ports.cmake around the port inclusion path to determine why vcpkg_cmake_configure is unavailable, then verify the fix by rerunning the reported installation on x64-windows.

Written by the indexing model from the issue text.