fix(windows): vendor audiopus_sys + patch libopus for clang-cl SIMD

cargo-xwin drives the Windows MSVC cross-compile via clang-cl, under
which CMake sets MSVC=1 — causing libopus 1.3.1's `if(NOT MSVC)` guards
to skip the per-file `-msse4.1` / `-mssse3` COMPILE_FLAGS that its x86
SIMD source files need. Clang-cl (unlike real cl.exe) still honors
Clang's target-feature system, so those files then fail to compile
with "always_inline function '_mm_cvtepi16_epi32' requires target
feature 'sse4.1'" errors across silk/NSQ_sse4_1.c, NSQ_del_dec_sse4_1.c,
and VQ_WMat_EC_sse4_1.c.

Earlier attempts to fix this downstream (cargo-xwin toolchain file,
override.cmake CMAKE_C_COMPILE_OBJECT <FLAGS> replace, CFLAGS env vars)
all failed because cargo-xwin rewrites override.cmake from scratch on
every `cargo xwin build` invocation and cmake-rs's -DCMAKE_C_FLAGS=
assembly happens before toolchain FORCE sets propagate.

Fixing it upstream at the source: vendor audiopus_sys 0.2.2 into
vendor/audiopus_sys, patch its bundled opus/CMakeLists.txt to introduce
an MSVC_CL var (true only when CMAKE_C_COMPILER_ID == "MSVC", i.e. real
cl.exe), and flip the eight `if(NOT MSVC)` SIMD guards to
`if(NOT MSVC_CL)`. Clang-cl then gets the GCC-style per-file flags and
the SSE4.1 sources build cleanly. Also flip the `if(MSVC)` global /arch
block at line 445 to `if(MSVC_CL)` so only cl.exe applies /arch:AVX and
clang-cl relies purely on per-file flags (no global/per-file mixing).

Wire via [patch.crates-io] in the workspace root Cargo.toml; the patch
is resolved relative to the workspace root as `vendor/audiopus_sys`.

Upstream context: xiph/opus#256, xiph/opus PR #257 (both stale).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

vendor/audiopus_sys/opus/win32/VS2015/common.props

@@ -0,0 +1,82 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project ToolsVersion="4.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <ImportGroup Label="PropertySheets" />
+  <PropertyGroup Label="UserMacros" />
+  <PropertyGroup>
+    <OutDir>$(Platform)\$(Configuration)\</OutDir>
+    <IntDir>$(Platform)\$(Configuration)\$(ProjectName)\</IntDir>
+    <CharacterSet Condition="'$(ConfigurationType)'=='Application'">Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Debug' or '$(Configuration)'=='DebugDLL' or '$(Configuration)'=='DebugDLL_fixed'">
+    <LinkIncremental>true</LinkIncremental>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <WholeProgramOptimization>false</WholeProgramOptimization>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)'=='Release' or '$(Configuration)'=='ReleaseDLL' or '$(Configuration)'=='ReleaseDLL_fixed'">
+    <LinkIncremental>false</LinkIncremental>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+  </PropertyGroup>
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <WarningLevel>Level3</WarningLevel>
+      <CompileAsManaged>false</CompileAsManaged>
+      <CompileAsWinRT>false</CompileAsWinRT>
+      <AdditionalIncludeDirectories>..\..;..\..\include;..\..\silk;..\..\celt;..\..\win32;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
+      <PreprocessorDefinitions>HAVE_CONFIG_H;_CRT_SECURE_NO_WARNINGS;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <RuntimeTypeInfo>false</RuntimeTypeInfo>
+      <OpenMPSupport>false</OpenMPSupport>
+    </ClCompile>
+    <Lib>
+      <SubSystem>Console</SubSystem>
+    </Lib>
+    <Link>
+      <LargeAddressAware>true</LargeAddressAware>
+      <SubSystem>Console</SubSystem>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)'=='Debug' or '$(Configuration)'=='DebugDLL' or '$(Configuration)'=='DebugDLL_fixed'">
+    <ClCompile>
+      <ControlFlowGuard>Guard</ControlFlowGuard>
+      <DebugInformationFormat>ProgramDatabase</DebugInformationFormat>
+      <EnableEnhancedInstructionSet Condition="'$(Platform)'=='Win32'">NoExtensions</EnableEnhancedInstructionSet>
+      <EnableParallelCodeGeneration>false</EnableParallelCodeGeneration>
+      <FloatingPointExceptions>true</FloatingPointExceptions>
+      <FunctionLevelLinking>false</FunctionLevelLinking>
+      <InlineFunctionExpansion>Disabled</InlineFunctionExpansion>
+      <MultiProcessorCompilation>false</MultiProcessorCompilation>
+      <OmitFramePointers>false</OmitFramePointers>
+      <Optimization>Disabled</Optimization>
+      <RuntimeLibrary Condition="'$(Configuration)'=='Debug'">MultiThreadedDebug</RuntimeLibrary>
+      <RuntimeLibrary Condition="'$(Configuration)'!='Debug'">MultiThreadedDebugDLL</RuntimeLibrary>
+      <SDLCheck>true</SDLCheck>
+      <StringPooling>false</StringPooling>
+    </ClCompile>
+    <Link>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)'=='Release' or '$(Configuration)'=='ReleaseDLL' or '$(Configuration)'=='ReleaseDLL_fixed'">
+    <ClCompile>
+      <ControlFlowGuard>false</ControlFlowGuard>
+      <DebugInformationFormat>None</DebugInformationFormat>
+      <EnableFiberSafeOptimizations>true</EnableFiberSafeOptimizations>
+      <EnableParallelCodeGeneration>true</EnableParallelCodeGeneration>
+      <ExceptionHandling>false</ExceptionHandling>
+      <FavorSizeOrSpeed>Speed</FavorSizeOrSpeed>
+      <FloatingPointModel Condition="'$(Configuration)'=='Release'">Fast</FloatingPointModel>
+      <FloatingPointModel Condition="'$(Configuration)'!='Release'">Precise</FloatingPointModel>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+      <MultiProcessorCompilation>true</MultiProcessorCompilation>
+      <Optimization>MaxSpeed</Optimization>
+      <RuntimeLibrary Condition="'$(Configuration)'=='Release'">MultiThreaded</RuntimeLibrary>
+      <RuntimeLibrary Condition="'$(Configuration)'!='Release'">MultiThreadedDLL</RuntimeLibrary>
+      <StructMemberAlignment>16Bytes</StructMemberAlignment>
+    </ClCompile>
+    <Link>
+      <GenerateDebugInformation>false</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemGroup />
+</Project>