--- src/corelib/tools/qsimd_p.h.orig	2017-09-06 05:13:54.000000000 -0700
+++ src/corelib/tools/qsimd_p.h	2021-01-12 23:42:29.000000000 -0600
@@ -329,7 +329,7 @@
     _BitScanForward(&result, val);
     return result;
 }
-#  elif (defined(Q_CC_CLANG) || (defined(Q_CC_GNU) && Q_CC_GNU < 405)) \
+#  elif ((defined(Q_CC_CLANG) && !defined(_bit_scan_reverse)) || (!defined(Q_CC_CLANG) && defined(Q_CC_GNU) && Q_CC_GNU < 405)) \
     && !defined(Q_CC_INTEL)
 // Clang is missing the intrinsic for _bit_scan_reverse
 // GCC only added it in version 4.5