Experimental common-symbols patch

[Zack Weinberg <zack@rabi.columbia.edu>]

There was some discussion awhile back about getting rid of the need
for the intermediate link step in the build of libc.so and ld.so.
It's there because we don't want to have common symbols shared between
libc.so and ld.so.  The appended patch makes all the common symbols
that appear on an x86/linux build into proper globals, defined in one
file and referenced via 'extern' elsewhere.  That should allow us to
dump the intermediate pass.

The patch is experimental: it doesn't appear to break anything (full
build and check completes fine), but I want to get some more testing
before proposing it for inclusion.  In particular, I'm sure I've
missed common symbols that occur on other platforms.  If people with
non-x86 systems could build libc with this patch applied and then send
me the output of

nm -o libc_pic.a elf/dl-allobjs.os |grep ' C '

I would appreciate it.  You may see warnings about missing braces on
initializers; those will be fixed in the next revision. I haven't
changed the makefiles yet.

zw

application/gzip