[Patch, Fortran] PR 47569 - fix ICE (regression) and fix diagnostic

[Tobias Burnus]

PR 47569 is about a 4.3/4.4/4.5/4.6 regression where 
"component%substring(1:2)" gave an ICE. Looking closer at the issue, I 
saw that the checks were a bit incomplete and inconsistent. I hope that 
with the patch the diagnostic is now correct.

 From the standards:

F97: "If the actual argument is scalar, the corresponding dummy argument 
shall be scalar unless the actual argument is an element of an array 
that is not an assumed-shape or pointer array, or a substring of such an 
element."

F2003: "If the actual argument is scalar, the corresponding dummy 
argument shall be scalar unless the actual argument is of type default 
character, of type character with the C character kind (15.1), or is an 
element or substring of an element of an array that is not an 
assumed-shape or pointer array."

F2008 quote ("12.5.2.4 Ordinary dummy variables"):
"If the actual argument is a noncoindexed scalar, the corresponding dummy
argument shall be scalar unless the actual argument is default character, of
type character with the C character kind (15.2.2), or is an element or
substring of an element of an array that is not an assumed-shape, 
pointer, or
polymorphic array."

(The coindex/polymorphism is checked earlier in that function.)

Build and regtested on x86-64-linux.
OK for the trunk? Should this be backported? If yes, to which versions?*

Tobias

* The issue was reported for a real-world code using GCC 4.4.4. While 
passing a scalar actual to an array dummy is common in pre-Fortran-90, I 
think doing so in F90+ code happens more rarely - but as the PR shows, 
it happens.
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