A SSE2 only CPU was reported to the guest as a SSE3 CPU.

A SSE2 only CPU was reported to the guest as a SSE3 CPU.
The guest code might then select functions calling invalid
instructions.
E.G. giving:
  vex x86->IR: unhandled instruction bytes: 0x66 0xF 0x3A 0xF
  ==13094== valgrind: Unrecognised instruction at address 0x496d4d3.
  ==13094==    at 0x496D4D3: __mempcpy_ssse3 (memcpy-ssse3.S:771)
  ==13094==    by 0x125E0B: ??? (in /bin/dash)
as the host hw cap is not SSE3 enabled, while the guest believes
SSE3 can be used.

So, change CPUID so as to report an SSE3 if the hw is SSE3,
and otherwise SSE1 or lower.

(an SSE2 cpu might be added later on)

git-svn-id: svn://svn.valgrind.org/vex/trunk@3153