[testsuite] Fix multiple definitions of _init

[Oleg Endo]

On Mon, 2014-12-01 at 12:09 +0100, Richard Biener wrote:
> On Mon, Dec 1, 2014 at 8:21 AM, Oleg Endo <oleg.endo@t-online.de> wrote:
> > Hi,
> >
> > When running the testsuite on a sh-elf configuration, some test cases
> > fail due to multiple definitions of the function '_init'.  This is
> > because on sh-elf every function is automatically prefixed with a '_'
> > char.  When defining a C function 'init' in some code, the actual name
> > becomes '_init' and this conflicts with the _init function in libgcc
> > (crti.S).  While the behavior of adding the '_' prefix is debatable, the
> > testsuite failures can be easily fixed by the attached patch.
> > Is this OK for trunk?
> 
> The testcases are certainly valid C testcases and thus sh-elf is buggy
> here.  As '_init' is a reserved identifier it shouldn't mangle 'init' as
> '_init'.
> 
> Do you never run into "real" applications naming a function 'init'?

Looking for USER_LABEL_PREFIX shows that the '_' prefix mangling scheme
is being used by quite some targets/configs.  So it's not just sh-elf,
but other bare metal configs and their ABIs, where 'init' gets mangled
to '_init' and there's a '.global _init' in libgcc.  Yes, it does break
valid standard C code 'void init (void)', but it's been doing that for
quite a while.

I didn't mean to open a can of worms because of 4 test cases showing up
in sh-elf sim tests.  From what I can see, those 4 cases would also pop
up for other configs, not only sh-elf.  Anyway, the function names in
those test cases don't matter at all, do they?

Cheers,
Oleg