.SUFFIXES hosed by switch to automake 1.9.x

[Ralf Corsepius]

On Tue, 2007-04-17 at 23:38 +0100, Joern Rennecke wrote:
> Before the switch to automake 1.9.x, the .SUFFIXES rule in
> newlib/libc/sys/arc/Makefile.in was:
> .SUFFIXES: .S .c .o .s
> Since the switch to automake 1.9.x on 11 April 2006, this rule now reads:
> .SUFFIXES: .c .o .obj
> 
> which breaks building crt0.o , since now there is no rule to build it from
> crt0.S .

Add *.S to *_SOURCES.

Unlike previous automakes (which didn't handle them), newer automakes
know to handle them.

Ralf