Fix type of extern array declared in inner scope with outer initialization shadowed...

Fix type of extern array declared in inner scope with outer initialization shadowed (PR c/88584).

As reported in bug 88584, if you have a file-scope array with external
linkage, initialized at file scope, and that array is shadowed at
block scope, and is declared again with external linkage and an
incomplete type in an inner scope, it is wrongly given a complete type
in that inner scope when the correct C semantics give it an incomplete
type (only the visible declarations contribute to the type in a given
scope).

In general, issues with the types of external linkage declarations
being different in different scopes were addressed by my fixes for bug
13801, for GCC 4.0.  In this case, however, the code in pushdecl
dealing with giving declarations the right type in each scope works
fine, and the type is subsequently modified by complete_array_type
called from finish_decl: finish_decl is trying to complete an array
type based on an initializer, but that's only correct for the original
initialization at file scope, not for such a declaration in an inner
scope (it's harmless but unnecessary in the case where the original
declaration is still visible in the inner scope).  Thus, this patch
changes finish_decl to stop this logic applying for such an external
declaration in an inner scope.  (An erroneous attempt to include an
initializer for an extern variable in an inner scope is diagnosed
elsewhere.)

This is a regression from GCC 3.4, which properly rejected the code in
question (quite likely by accident).

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc/c:
	PR c/88584
	* c-decl.c (finish_decl): Do not complete array types for arrays
	with external linkage not at file scope.

gcc/testsuite:
	PR c/88584
	* gcc.dg/redecl-18.c: New test.

From-SVN: r268571