Fix building with clang_cl

Clang reports itself as MSVC but doesn't allow intrinsics to be used
unconditionally independent of command-line flags like MSVC does.

Fixes: QTBUG-68551
Change-Id: I65d1ee1aa5c02b7c3a25c10c69c3d5e88129b858
Reviewed-by: Eirik Aavitsland <[email protected]>

Author: Allan Sandfeld Jensen

src/3rdparty/libwebp/src/dsp/dsp.h

@@ -55,12 +55,12 @@ extern "C" {
 #if !defined(EMSCRIPTEN)
 
 #if defined(_MSC_VER) && _MSC_VER > 1310 && \
-    (defined(_M_X64) || defined(_M_IX86))
+    (defined(_M_X64) || defined(_M_IX86)) && !defined(__clang__)
 #define WEBP_MSC_SSE2  // Visual C++ SSE2 targets
 #endif
 
 #if defined(_MSC_VER) && _MSC_VER >= 1500 && \
-    (defined(_M_X64) || defined(_M_IX86))
+    (defined(_M_X64) || defined(_M_IX86)) && !defined(__clang__)
 #define WEBP_MSC_SSE41  // Visual C++ SSE4.1 targets
 #endif
 
@@ -90,7 +90,7 @@ extern "C" {
 #define WEBP_USE_NEON
 #endif
 
-#if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_M_ARM)
+#if defined(_MSC_VER) && _MSC_VER >= 1700 && defined(_M_ARM) && !defined(__clang__)
 #define WEBP_USE_NEON
 #define WEBP_USE_INTRINSICS
 #endif