Mark static mm_load8_zero_extend [[maybe_unused]]

static Q_ALWAYS_INLINE __m128i mm_load8_zero_extend(const void *ptr)
is unused when compiled on Android.
This causes a compiler warning and blocks CI, if compiled with -Werror.

This patch marks the method [[maybe_unused]], in order to prevent the
warning.

Change-Id: Ife10c0a84ac34196405ce9c2356351d825751adb
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/corelib/text/qstring.cpp

@@ -400,6 +400,7 @@ static constexpr bool UseSse4_1 = bool(qCompilerCpuFeatures & CpuFeatureSSE4_1);
 static constexpr bool UseAvx2 = UseSse4_1 &&
         (qCompilerCpuFeatures & CpuFeatureArchHaswell) == CpuFeatureArchHaswell;
 
+[[maybe_unused]]
 static Q_ALWAYS_INLINE __m128i mm_load8_zero_extend(const void *ptr)
 {
     const __m128i *dataptr = static_cast<const __m128i *>(ptr);