[Bug c++/70576] New: G++ compiles and links invalid code when shadowing global function in function scope

["jaak at ristioja dot ee" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70576

            Bug ID: 70576
           Summary: G++ compiles and links invalid code when shadowing
                    global function in function scope
           Product: gcc
           Version: 5.3.0
            Status: UNCONFIRMED
          Severity: major
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jaak at ristioja dot ee
  Target Milestone: ---

int foo() { return 2; }
int main() {
  int& foo();
  foo() = 42; // Segfault
}

First detected here:
https://stackoverflow.com/questions/36477542/what-does-int-foo-mean-in-c

Compiles with GCC 4.7.4, 4.8.5, 4.9.3 and 5.3.0 without any warnings with -Wall
-Wextra -Wshadow.

Clang errors with:

test.cpp:3:8: error: functions that differ only in their return type cannot be
overloaded
  int& foo();
  ~~~~ ^
test.cpp:1:5: note: previous definition is here