[Bug debug/102978] New: Function/Struct declaration with absent semicolon that is put before including standard header results in wall of errors with no indication of the actual problem

[konstantinua00 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102978

            Bug ID: 102978
           Summary: Function/Struct declaration with absent semicolon that
                    is put before including standard header results in
                    wall of errors with no indication of the actual
                    problem
           Product: gcc
           Version: 11.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: debug
          Assignee: unassigned at gcc dot gnu.org
          Reporter: konstantinua00 at gmail dot com
  Target Milestone: ---

```
void foo()
#include <any_std_header>
```
or
```
struct bar
#include <any_std_header>
```
as stated, give many useless errors.

example with <bitset>: https://godbolt.org/z/KbrrszEWr  
less intimidating example with <cstddef>: https://godbolt.org/z/hxnxzqTcW
example with struct declaration: https://godbolt.org/z/nhTKc8cM9
happens in GCC with C std header too: https://godbolt.org/z/c6hMWexcW

Such situation happens when there're 2 user headers: first with missing
semicolon and second with new-in-TU std header.

G++(but not GCC) already notices missing semicolon on struct definitions and
GCC (but not G++) notices globals without one (due to typedef 
https://godbolt.org/z/44oYT1PKn), so maybe something can be done for
declarations too?