Make vector allocation aligned to 64-bytes (#1909)

* Make vector allocation aligned to 64-bytes as that is the same alignement requirement used by State data.

* Add release note.

---------

Co-authored-by: Jun Doi <doichan@jp.ibm.com>

releasenotes/notes/fix-aer-vector-alignment-aace6e14342c002e.yaml

@@ -0,0 +1,10 @@
+---
+fixes:
+  - |
+    Change ``AER::Vector`` object alignement to 64-byte. In some cases, it is used to 
+    initialize ``AER:QV::QubitVector`` objects by moving storage ownership to these 
+    objects. As the code assumes that ``AER:QV::QubitVector`` storage is at least 
+    32-byte aligned for AVX2 load instructions, this change enforces the same alignement 
+    requirements for both  ``AER::Vector`` and  ``AER:QV::QubitVector`` objects so that 
+    one doesn't get into segmentation faults.
+    

src/framework/linalg/vector.hpp

@@ -31,7 +31,15 @@ namespace AER {
 
 template <class T>
 T *malloc_data(size_t size) {
+#if !defined(_WIN64) && !defined(_WIN32)
+  // Data allocated here may need to be properly aligned to be compliant with
+  // AVX2.
+  void *data = nullptr;
+  posix_memalign(&data, 64, sizeof(T) * size);
+  return reinterpret_cast<T *>(data);
+#else
   return reinterpret_cast<T *>(malloc(sizeof(T) * size));
+#endif
 }
 
 template <class T>