ubsan: misaligned load in QString simd code

UBSan error:

/home/marc/Qt/qtbase/src/corelib/tools/qstring.cpp:581:42: runtime error: load of misaligned address 0x2aee7eeac8d3 for type 'const long long int', which requires 8 byte alignment
0x2aee7eeac8d3: note: pointer points here
 36  34 29 00 6c 6f 63 61 6c  68 6f 73 74 00 64 65 62  75 67 70 69 70 65 00 53  6f 63 6b 65 74 20 65
              ^ 

(the line number may be off by now)

It might be a false positive, but ubsan is usually very, very careful not to report false positives. Even if it is a FP, it needs to be fixed or worked around, since it actively thwards higher-level ubsan debugging.

To reproduce, compile with -sanitize-undefined and run, e.g. tests/auto/corelib/kernel/qeventloop (to name just the first test that triggers it for me)