[clang][Interp] Remove now faulty assertion

We can call getBase() for pointers where Base != Offset as well,
for example when we've added a constant to the Offset.

clang/lib/AST/Interp/Pointer.h

@@ -215,7 +215,6 @@ class Pointer {
       assert(Offset == PastEndMark && "cannot get base of a block");
       return Pointer(Pointee, Base, 0);
     }
-    assert(Offset == Base && "not an inner field");
     unsigned NewBase = Base - getInlineDesc()->Offset;
     return Pointer(Pointee, NewBase, NewBase);
   }

clang/test/AST/Interp/cxx11.cpp

@@ -22,3 +22,9 @@ int array2[recurse2]; // both-warning {{variable length arrays in C++}} \
                       // both-note {{initializer of 'recurse2' is not a constant expression}} \
                       // expected-error {{variable length array declaration not allowed at file scope}} \
                       // ref-warning {{variable length array folded to constant array as an extension}}
+
+struct S {
+  int m;
+};
+constexpr S s = { 5 };
+constexpr const int *p = &s.m + 1;