Add blendZero operation with two ivec4s to blend two masks

This is not added in SSE, because comparing two fvec4s results in an
fvec4, not an ivec4

openmmapi/include/openmm/internal/vectorize_neon.h

@@ -426,6 +426,10 @@ static inline fvec4 blendZero(fvec4 v, ivec4 mask) {
     return blend(0.0f, v, mask);
 }
 
+static inline ivec4 blendZero(ivec4 v, ivec4 mask) {
+    return v & mask;
+}
+
 // These are at the end since they involve other functions defined above.
 
 static inline fvec4 round(fvec4 v) {

openmmapi/include/openmm/internal/vectorize_pnacl.h

@@ -369,6 +369,10 @@ static inline fvec4 blendZero(fvec4 v, ivec4 mask) {
     return blend(0.0f, v, mask);
 }
 
+static inline ivec4 blendZero(ivec4 v, ivec4 mask) {
+    return v & mask;
+}
+
 // These are at the end since they involve other functions defined above.
 
 static inline fvec4 min(fvec4 v1, fvec4 v2) {

openmmapi/include/openmm/internal/vectorize_ppc.h

@@ -375,6 +375,10 @@ static inline fvec4 blendZero(fvec4 v, ivec4 mask) {
     return blend(0.0f, v, mask);
 }
 
+static inline ivec4 blendZero(ivec4 v, ivec4 mask) {
+    return v & mask;
+}
+
 // These are at the end since they involve other functions defined above.
 
 static inline fvec4 min(fvec4 v1, fvec4 v2) {