Instead of compiling files with -fcommon, create an include file and declare
the 3 symbols that need to be common using an attribute. Put all the 3 symbol
definitions in libc in one place (initfini.c). Reviewed by joerg@

Provide symbol definitions for environ and __progname. These are duplicate
definitions to the ones provided by csu, but harmless since the linker resolves
them. There are 3 non weak data symbols provided in crt0.o:

D __progname [initialized data, assigned to ""]
B __ps_strings [BSS since assigned to 0]
C environ [common, uninitialized]

__ps_strings had already a second definition in libc (in BSS), now we added
__progname and __ps_strings (in BSS).

To get rid of the duplicate definition, we can remove them from csu, and
move the assignments to libc.

This is done so that libc has no undefined symbols so that linker maps
that want to do:
...
local:
*;
...
don't end up producing link failures for libc.

netbsd.org->NetBSD.org

Don't need to include <string.h>.

branches: 1.1.2;
add getprogname() and setprogname(). These allow uses of __progname to
be wrapped in some sane fashion, for portability.