Small change in NSObject.m ASM needed for PowerPC build

[Eric Wasylishen]

Hi,
I ran in to a small problem when compiling GNUstep (svn trunk) on
Debian testing for PowerPC. GCC is "gcc (Debian 4.3.2-1.1) 4.3.2"

Compiling file NSObject.m ...
/tmp/ccF8zgwE.s: Assembler messages:
/tmp/ccF8zgwE.s:730: Error: symbol `modified' is already defined
make[3]: *** [obj/NSObject.m.o] Error 1

The PPC atomic increment and decrement functions starting at line 254
of NSObject.m both use the label 'modified:' in their asm code. I
found that by changing the labels in one of the functions to something
else ("modified2"), this error disappeared.

I'm not sure if GCC is correct in reporting this as an error or not,
but it's easy to fix.
-Eric