Clear MMX FP state in PVQ code.

Not clearing the FP state was causing acos to return NaN on OSX / LLVM.
This was not causing problems Linux or AWCY.

Change-Id: I278d02839e4de858b5f55cfb380fa3968937995e

av1/decoder/pvq_decoder.c

@@ -26,6 +26,7 @@
 #include "av1/common/pvq_state.h"
 #include "av1/decoder/decint.h"
 #include "av1/decoder/pvq_decoder.h"
+#include "aom_ports/system_state.h"
 
 static void aom_decode_pvq_codeword(aom_reader *r, od_pvq_codeword_ctx *ctx,
  od_coeff *y, int n, int k) {
@@ -319,6 +320,8 @@ void od_pvq_decode(daala_dec_ctx *dec,
   const unsigned char *pvq_qm;
   int use_masking;
 
+  aom_clear_system_state();
+
   /*Default to skip=1 and noref=0 for all bands.*/
   for (i = 0; i < PVQ_MAX_PARTITIONS; i++) {
     noref[i] = 0;

av1/encoder/pvq_encoder.c

@@ -26,6 +26,7 @@
 #include "av1/common/pvq_state.h"
 #include "av1/encoder/encodemb.h"
 #include "av1/encoder/pvq_encoder.h"
+#include "aom_ports/system_state.h"
 
 #define OD_PVQ_RATE_APPROX (0)
 /*Shift to ensure that the upper bound (i.e. for the max blocksize) of the
@@ -825,6 +826,8 @@ PVQ_SKIP_TYPE od_pvq_encode(daala_enc_ctx *enc,
   OD_UNUSED(by);
 #endif
 
+  aom_clear_system_state();
+
   use_masking = enc->use_activity_masking;
 
   if (use_masking)