[PATCH] obvious pattern fix in gdb.base/step-line.exp

[Christophe LYON]

> 
>> I'm OK with leaving the testcase untouched if we don't need to.
> OK. So I won't commit my patch, and fix the compiler instead.
> 

I have been trying to fix the compiler so that it behaves like GCC 
(using 2 separate filenames for the actual source file and for the one 
provided with #line), but I get regressions later in step-line.exp.

After dumping the debug_line info (with readelf and/or dwarfdump), I 
mostly noticed that the file number has changed according to the 
compiler fix.

However, from GDB, using "maintenance print symbols", I noticed that 
quite a few lines have become "0" instead of meaningful values. In turn, 
I thinks this makes skip_prologue do something wrong.

What I dont' understand currently is where those "0" line entries come 
from? Is there any verbose flag or maintenance command I could use to 
understand how the Dwarf debug_line info is parsed?

Thanks,

Christophe.