[Patch, Fortran] PR34899 - Support <tab><digit> as continuation line marker (fixed form)

[Tobias Burnus]

In standard fixed-form Fortran source code, a "normal" line begins with 
6 spaces and a continuation line with 5 spaces plus some character such 
as '*' (there are some restrictions, see F95/F2003 standard).

A very common vendor extension is to support <tab> as replacement for 6 
spaces, which also gfortran supports. However, how to create then a 
continuation line? Well, for g77, NAG f95, ifort, openf95, sunf95, 
pathscale, pgf95, Absoft the answer is: <tab><digit> where digit is not 
zero.

The attached patch now does the following: It replaces '\t' by 6 spaces 
(before it was 7) and if the the tab is followed by a non-zero digit, it 
places it at position 6.


Build and regression tested on x86-64-linux.
OK for the trunk?

Tobias


PS: The patch was motivated to get to build 
http://www.chara.gsu.edu/~gudehus/fits_library_package.html. However, 
due to other problems it still won't build. gfortran stops first for 
integer_var = .true. (unless -std=legacy) and then for "real_var = ' '". 
Replacing them by transfer it stops at the same line as ifort.


PPS: There are dozens of possibilities with <tab><digit>, which are 
differently treated with the different compilers, e.g. " <tab><digit>" 
or "<tab> <digit>", where different compilers produce different results. 
With this patch " <tab><digit>" is supported while "<tab> <digit>" is 
rejected. The latter is in line with ifort but a regression with regards 
to g77, which I believe we can ignore.
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