Fix weak stub of _sbrk_r()
Fix weak stub of _sbrk_r()

When LTO is enabled a "warning: '_sbrk_r' violates the C++ One
Definition Rule  [-Wodr]" is generated, because the weak stub returns
"caddr_t", while the real implementation - "void*". Use "void*" in both
places, which is also consistent with the type used internally by
newlib.
jasmin-j/distortos,jasmin-j/distortos,jasmin-j/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,DISTORTEC/distortos,jasmin-j/distortos,CezaryGapinski/distortos,DISTORTEC/distortos,CezaryGapinski/distortos,DISTORTEC/distortos,jasmin-j/distortos,CezaryGapinski/distortos,CezaryGapinski/distortos