d3d11va: Check WINAPI_FAMILY instead of HAVE_LOADLIBRARY

If using the winstore compat library, a fallback LoadLibrary
function does exist, that only calls LoadPackagedLibrary though
(which doesn't work for dynamically loading d3d11 DLLs).

Therefore explicitly check the targeted API family instead.

Make this check a reusable HAVE_* component which other parts
of the libraries can check when necessary as well.
Signed-off-by: Martin Storsjö <martin@martin.st>

configure

@@ -1720,6 +1720,7 @@ HAVE_LIST="
     sdl
     section_data_rel_ro
     threads
+    uwp
     vaapi_drm
     vaapi_x11
     vdpau_x11
@@ -4894,7 +4895,18 @@ fi
 
 # d3d11va requires linking directly to dxgi and d3d11 if not building for
 # the desktop api partition
-enabled LoadLibrary || d3d11va_extralibs="-ldxgi -ld3d11"
+check_cpp <<EOF && enable uwp && d3d11va_extralibs="-ldxgi -ld3d11"
+#ifdef WINAPI_FAMILY
+#include <winapifamily.h>
+#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+#error desktop, not uwp
+#else
+// WINAPI_FAMILY_APP, WINAPI_FAMILY_PHONE_APP => UWP
+#endif
+#else
+#error no family set
+#endif
+EOF
 
 enabled vaapi && require vaapi va/va.h vaInitialize -lva
 

libavutil/hwcontext_d3d11va.c

@@ -56,7 +56,7 @@ static PFN_D3D11_CREATE_DEVICE mD3D11CreateDevice;
 
 static av_cold void load_functions(void)
 {
-#if HAVE_LOADLIBRARY
+#if !HAVE_UWP
     // We let these "leak" - this is fine, as unloading has no great benefit, and
     // Windows will mark a DLL as loaded forever if its internal refcount overflows
     // from too many LoadLibrary calls.
@@ -486,7 +486,7 @@ static int d3d11va_device_create(AVHWDeviceContext *ctx, const char *device,
     int ret;
 
     // (On UWP we can't check this.)
-#if HAVE_LOADLIBRARY
+#if !HAVE_UWP
     if (!LoadLibrary("d3d11_1sdklayers.dll"))
         is_debug = 0;
 #endif
@@ -527,7 +527,7 @@ static int d3d11va_device_create(AVHWDeviceContext *ctx, const char *device,
         ID3D10Multithread_Release(pMultithread);
     }
 
-#if HAVE_LOADLIBRARY && HAVE_DXGIDEBUG_H
+#if !HAVE_UWP && HAVE_DXGIDEBUG_H
     if (is_debug) {
         HANDLE dxgidebug_dll = LoadLibrary("dxgidebug.dll");
         if (dxgidebug_dll) {