DynamoRIO mixes Intel AVX and Intel SSE code

As mentioned on [Intel optimization manual](https://www.intel.com/content/dam/www/public/us/en/documents/manuals/64-ia-32-architectures-optimization-manual.pdf) in "Mixing AVX code with SSE code" section:

> If software inter-mixes AVX and SSE instructions without using VZEROUPPER properly, it can experience an AVX/SSE transition penalty

I have noticed that this causes a significant performance regression when running DynamoRIO on Intel Skylake (model 85)

For instance, taking into account an application which performs a simple for loop, compiled with `-ftree-vectorize -O3`:

```
int N=10000;

__attribute__((noinline)) void vector_triad(const double* __restrict a, const double* __restrict b, double* __restrict c, double scale){
//__asm__("vzeroupper");
for(int i=0; i 0m2.844s`

`time drrun -- app --> 0m14.376s`

When instead running the same application adding the "vzeroupper" command (reported in the code as comment):

`time drrun -- app --> 0m3.225s`

Is there a fix that could be implemented inside DynamoRIO in order to prevent such slowdown?