Fix clang-cl build with disabled x86 intrinsics

clang-cl's intrinsics support is broken, it doesn't declare the AVX2
intrinsics if they are disabled and this doesn't match GCC or MSVC
behavior: https://github.com/llvm/llvm-project/issues/53520

This fix allows to disable x86 intrinsiscs during configuration of
clang-cl build.

clang-cl build is still not guaranteed to work with enabled x86 intrinsics.

Change-Id: Icd295f6b4d868adf10bcd425d5280c56b43cb9f7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

configure.cmake

@@ -1274,6 +1274,16 @@ if (TEST_architecture_arch STREQUAL x86_64 OR TEST_architecture_arch STREQUAL i3
             MESSAGE [=[
 All x86 intrinsics and SIMD support were disabled. If this was in error, check
 the result of the build in config.tests/x86intrin and report at https://bugreports.qt.io.
+]=]
+        )
+    elseif (MSVC AND CLANG)
+        # Warn only
+        qt_configure_add_report_entry(
+            TYPE WARNING
+            CONDITION (NOT QT_FEATURE_x86intrin)
+            MESSAGE [=[
+x86 intrinsics support is disabled for clang-cl build. This might be necessary due to
+https://github.com/llvm/llvm-project/issues/53520
 ]=]
         )
     else()

src/corelib/global/qnumeric_p.h

@@ -180,7 +180,7 @@ static inline bool convertDoubleTo(double v, T *value, bool allow_precision_upgr
     // correct, but Clang, ICC and MSVC don't realize that it's a constant and
     // the math call stays in the compiled code.
 
-#ifdef Q_PROCESSOR_X86_64
+#if defined(Q_PROCESSOR_X86_64) && defined(__SSE2__)
     // Of course, UB doesn't apply if we use intrinsics, in which case we are
     // allowed to dpeend on exactly the processor's behavior. This
     // implementation uses the truncating conversions from Scalar Double to

src/corelib/global/qsimd.h

@@ -55,7 +55,7 @@
 
 #if defined(Q_PROCESSOR_X86) && defined(Q_CC_MSVC)
 // MSVC doesn't define __SSE2__, so do it ourselves
-#  if (defined(_M_X64) || _M_IX86_FP >= 2)
+#  if (defined(_M_X64) || _M_IX86_FP >= 2) && defined(QT_COMPILER_SUPPORTS_SSE2)
 #    define __SSE__ 1
 #    define __SSE2__ 1
 #  endif