[flang][semantics] `implicit none` may leak to other program units

[foxtran]

With the following example:

module t
  common /fmcom2/ e, z(1)
end module t
subroutine test(n)
  use t
  implicit none
  integer :: n
end subroutine test

flang produces the following output:

error: Semantic errors in /app/example.f90
/app/example.f90:2:19: error: No explicit type declared for 'e'
    common /fmcom2/ e, z(1)
                    ^
/app/example.f90:2:22: error: No explicit type declared for 'z'
    common /fmcom2/ e, z(1)
                       ^
Compiler returned: 1

Flang version:

flang version 22.0.0git (https://github.com/llvm/llvm-project.git 678dcf13d8fa9c1e5086864ff998e068cbb3160c)
Target: x86_64-unknown-linux-gnu
Thread model: posix

Example on godbolt:

https://godbolt.org/z/zM7W6z5sd

[llvmbot]

@llvm/issue-subscribers-flang-frontend

Author: foxtran (foxtran)

With the following example: ``` module t common /fmcom2/ e, z(1) end module t subroutine test(n) use t implicit none integer :: n end subroutine test ``` flang produces the following output: ``` error: Semantic errors in /app/example.f90 /app/example.f90:2:19: error: No explicit type declared for 'e' common /fmcom2/ e, z(1) ^ /app/example.f90:2:22: error: No explicit type declared for 'z' common /fmcom2/ e, z(1) ^ Compiler returned: 1 ```

Flang version:

flang version 22.0.0git (https://github.com/llvm/llvm-project.git 678dcf13d8fa9c1e5086864ff998e068cbb3160c)
Target: x86_64-unknown-linux-gnu
Thread model: posix

Example on godbolt:

https://godbolt.org/z/zM7W6z5sd