[V7][PATCH 0/2]Accept and Handle the case when a structure including a FAM nested in another structure

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

Hi,

This is the 7th version of the patch, which rebased on the latest trunk.
This is an important patch needed by Linux Kernel security project. 

We already have an extensive discussion on this issue and I have went
through 6 revisions of the patches based on the discussion and resolved
all the comments and suggestions raised during the discussion;

compared to the 6th version, the major change are:

1. update the documentation to replace the mentioning of GCC14 with
GCC15.
2. update the documentation to replace the following wording:
"A structure or a union with a C99 flexible array member"
with:
"A structure containing a C99 flexible array member, or a union containing
such a structure,"

All others are the same as 6th version. 

the 6th version are here:

https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616312.html
https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616313.html
https://gcc.gnu.org/pipermail/gcc-patches/2023-April/616314.html

Kees has tested the 6th version of the patch with Linux kernel, and everything
is good. relsolved many false positives for bounds checking.

Notes for the review history of these patches (2 patches)
1.The patch 1/2: Handle component_ref to a structre/union field including
  flexible array member [PR101832]

   The C front-end part has been approved by Joseph.
   For the middle-end, most of the change has been reviewed by Richard
   (and modified based on his comments and suggestions), except the change
   in tree-object-size.cc.
  
2.The patch 2/2: Update documentation to clarify a GCC extension

   This is basically a C FE and documentation change, I have updated it based
   on previous comments and suggestions.
   Joseph, could you review it to see whether this version is ready to go?

bootstrapped and regression tested on aarch64 and x86.

Okay for commit?

thanks a lot.

Qing

(for more details on the review history, I listed other important notes
below:


A. Richard Biener has reviewed the middle-end part of the first patch 
and raised some comments for the 4th version:
https://gcc.gnu.org/pipermail/gcc-patches/2023-March/613643.html

I updated it with his suggestion and Sandra’s comments as 5th version:
https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614100.html

B. The comments for the 5th version:
https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614511.html
(In this one, Joseph approved the C FE change of the first patch).
https://gcc.gnu.org/pipermail/gcc-patches/2023-March/614514.html
(In this one, Joseph raised two comments on the documentation wordings
 for the 2nd patch. And I updated  based on his comment in the 6th version)
)