Dear all,

compile time simplification of INDEX(str1,str2,back=.true.) gave wrong
results.  Looking at gfc_simplify_index, this appeared to be close to
a complete mess, while the runtime library code - which was developed
later - was a relief.

The solution is to use the runtime library code as template to fix this.
I took the opportunity to change string index and length variables
in gfc_simplify_index to HOST_WIDE_INT.

Regtested on x86_64-pc-linux-gnu.  OK for mainline?

As this is a wrong-code issue, would this qualify for backports to
open branches?

Thanks,
Harald