Out-of-bounds memcpy on ppc64le

Hello,

with GCC10.x and Vala 0.48.10 (also seems to apply for older Vala versions) compiling Vala's tests fails on ppc64le:

basic_types_arrays.c:1268:2: error: 'memcpy' forming offset [8, 23] is
out of the bounds [0, 8] [-Werror=array-bounds]
 1268 |  memcpy (dup, self, sizeof (Foo));
      |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~