Bug or feature - merging linkage declarations from static forced-inline functions

[Freddie Chopin]

Here's a minimal test case:

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$ cat test.cpp

extern "C"
{

void f1()
{
  union some_type{
    char a[2];
    int b;
  } variable;
}

void f2()
{
  union some_type{
    char a[2];
    int b;
  } variable;
}

}

$ arm-none-eabi-gcc test.cpp -c
test.cpp: In function 'void f2()':
test.cpp:17:5: warning: conflicting C language linkage declaration
'f2()::some_type variable'
   } variable;
     ^~~~~~~~
test.cpp:9:5: note: previous declaration 'f1()::some_type variable'
   } variable;
     ^~~~~~~~

$ arm-none-eabi-gcc --version
arm-none-eabi-gcc (bleeding-edge-toolchain) 8.0.1 20180427 (prerelease)
Copyright (C) 2018 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is
NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
PURPOSE.

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For the problem to appear:
- functions with the types and variables have to be extern "C"
- the file must be C++
- there has to be both a type and a variable
- the variables must have identical names

Any idea whether GCC is correct in this case or maybe the error is in
the headers?

Regards,
FCh