cc1 of nonexistent file still segfaults

[Per Bothner]

Daniel Berlin wrote:

> Daniel-Berlins-Computer:~/gcc/build/gcc dberlin$ ./cc1 -O1 nonexistent.c
> cc1: nonexistent.c: No such file or directory
> cc1: internal compiler error: Bus error

I'm vacationing at my parents, so it's awkeard to develop a fix.
It look like we should either test no_backend more toplev.c
or make sure to set errorcount when we fail to open the file.
-- 
	--Per Bothner
per@bothner.com   http://per.bothner.com/