Bitmap<128>::merge etc may crash on older GCC versions

Older GCC incorrectly optimizes Bitmap<128> code by using SSE instructions on unaligned data.
Analysis, by vlad.lesin

The compiller error was found on Ubuntu 16.04, CentOS 6/7.
To optimize the work with Bitmap<128>::buffer[] compiller uses sse instructions.
For example, the following C++ code:

-------------
void intersect(Bitmap & map2)

{ for (uint i = 0; i < array_elements(buffer); i++) buffer[i] &= map2.buffer[i]; }

-------------

is compilled into the following instructions:

-------------
movdqu xmm0,XMMWORD PTR [r12+0x28]
pand xmm0,XMMWORD PTR [rbx+0x28]
-------------

The second operand of 'pand' instruction must be alligned to 16, otherwise
exception occurs. But compiller generates the above instruction with
non-alligned second argument:

--------------
p ($rbx+0x28)%16
$20 = 8
--------------

There were also other instructions with non-alligned memory operand, for
example, 'por'.