tst_QByteArrayView:: disable failing constexpr checks for GCC

When comiling with ubsan, GCC is being too restrictive and ignores that
'static constexpr char []' can never be nullptr. It tries to evaluate
the comparison with nullptr, and fails with:

 error: ‘(((const char*)(& hello)) == 0)’ is not a constant

Disable the checks when compiling with GCC.

Fixes: QTBUG-101307
Pick-to: 6.3 6.2
Change-Id: I8322bb7cb326e06cd03b8b107c46a494c825087b
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

tests/auto/corelib/text/qbytearrayview/tst_qbytearrayview.cpp

@@ -270,6 +270,10 @@ void tst_QByteArrayView::constExpr() const
         static_assert(!bv2.empty());
         static_assert(bv2.size() == 5);
     }
+#if !defined(Q_CC_GNU) || defined(Q_CC_CLANG) || defined(Q_CC_INTEL)
+    // Below checks are disabled because of a compilation issue with GCC and
+    // -fsanitize=undefined. See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71962.
+    // Note: Q_CC_GNU is also defined for Clang and ICC, so we need to check those too.
     {
         static constexpr char hello[] = "Hello";
         constexpr QByteArrayView bv(hello);
@@ -304,6 +308,7 @@ void tst_QByteArrayView::constExpr() const
         static_assert(bv.back()  == 'o');
         static_assert(bv.last()  == 'o');
     }
+#endif
     {
         constexpr char *null = nullptr;
         constexpr QByteArrayView bv(null);