meson: Check d3d12video header for MinGW build

Old MinGW toolchain does not ship the header

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8400>

subprojects/gst-plugins-bad/sys/dwrite/meson.build

@@ -102,7 +102,7 @@ endif
 
 subdir('libcaption')
 
-if gstd3d12_dep.found() and cc.has_header('d3d11on12.h')
+if gstd3d12_dep.found() and cc.has_header('d3d11on12.h') and cc.has_header('d3d12video.h')
   extra_args += ['-DHAVE_GST_D3D12']
   extra_deps += [gstd3d12_dep]
   dwrite_sources += d3d12_sources

subprojects/gst-plugins-bad/sys/nvcodec/meson.build

@@ -99,7 +99,7 @@ if not nvbuf_dep.found()
   nvcodec_sources += nvcodec_dgpu_sources
 endif
 
-if gstd3d12_dep.found()
+if gstd3d12_dep.found() and cc.has_header('d3d12video.h')
   extra_args += ['-DHAVE_GST_D3D12']
   extra_deps += [gstd3d12_dep]
   nvcodec_sources += nvcodec_d3d12_sources

subprojects/gst-plugins-bad/sys/qsv/meson.build

@@ -84,7 +84,7 @@ if host_system == 'windows'
 
   qsv_sources += qsv_d3d11_sources
   qsv_platform_deps += [gstd3d11_dep]
-  if gstd3d12_dep.found()
+  if gstd3d12_dep.found() and cc.has_header('d3d12video.h')
     qsv_platform_deps += [gstd3d12_dep]
     extra_args += ['-DHAVE_GST_D3D12']
   endif