[v3][PATCH 0/2] Handle component_ref to a structure/union field including FAM for builtin_object_size

[Qing Zhao <qing.zhao@oracle.com>]

These are the 3rd version of the patches for PR101832, to fix
builtin_object_size to correctly handle component_ref to a
structure/union field that includes a flexible array member.

also includes a documentation update for the GCC extension on embedding
a structure/union with flexible array member into another structure.
which includes a fix to PR77650.

compared to the 2nd version of the patch, the major changes are:
1. only include C99 flexible array member to this extension, trailing [0], [1]
   and [4] are all excluded.
2. for the new bit type_include_flexarray in tree_type_common, print it
   and also stream in/out it. 
3. update testing cases.
4. more clarification on the documentation. warnings for deprecating the 
   case when the structure with C99 FAM is embedded in the middle of
   another structure. 
5. add a new warning option -Wgnu-variable-sized-type-not-at-end for
   identifing all such cases.

bootstrapped and regression tested on aarch64 and x86.

Okay for commit?

thanks.

Qing