Substrings were not reduced early enough for use in initializations,
such as DATA statements. Add an early simplification for substrings
with constant starting and ending points.
gcc/fortran/ChangeLog:
* gfortran.h (gfc_resolve_substring): Add prototype.
* primary.c (match_string_constant): Simplify substrings with
constant starting and ending points.
* resolve.c: Rename resolve_substring to gfc_resolve_substring.
(gfc_resolve_ref): Use renamed function gfc_resolve_substring.
gcc/testsuite/ChangeLog:
* substr_10.f90: New test.
* substr_9.f90: New test.