[sanitizer] [msan] Fix origin store of array types

This patch fixes the memory sanitizer origin store instrumentation for
array types.  This can be triggered by cases where frontend lowers
function return to array type instead of aggregation.

For instance, the C code:

--
struct mypair {
 int64_t x;
 int y;
};

mypair my_make_pair(int64_t x, int y)  {
 mypair p;
 p.x = x;
 p.y = y;
 return p;
}

int foo (int p)
{
  mypair z = my_make_pair(p, 0);
  return z.y + z.x;
}
--

It will be lowered with target set to aarch64-linux and -O0 to:

--
[...]
define i32 @_Z3fooi(i32 %p) #0 {
[...]
%call = call [2 x i64] @_Z12my_make_pairxi(i64 %conv, i32 0)
%1 = bitcast %struct.mypair* %z to [2 x i64]*
store [2 x i64] %call, [2 x i64]* %1, align 8
[...]
--

The origin store will emit a 'icmp' to test each store value again the
TLS origin array.  However since 'icmp' does not support ArrayType the
memory instrumentation phase will bail out with an error.

This patch change it by using the same strategy used for struct type on
array.

It fixes the 'test/msan/insertvalue_origin.cc' for aarch64 (the -O0 case).

llvm-svn: 257375