* Add assembly support routines from sdcc-svn/sdcc/device/lib/mos6502/ to gbdk-lib/libc/asm/mos6502/
* Add gbdk-lib/libc/asm/mos6502/Makefile, based on corresponding sm83 / z80 Makefiles
* Add CPU-specific include files to gbdk-lib/include/asm/mos6502/, based on corresponding sm83 / z80 include files
* Update gbdk-lib/include/asm/sm83/types.h and gbdk-lib/include/asm/z80.types.h to define REENTRANT as no-op
* Update gbdk-lib/include/stdio.h to use REENTRANT keyword for printf and sprintf
* Update gbdk-lib/include/stdlib.h to prevent #if-clause from redefining __reentrant as a no-op
* Update gbdk-lib/include/stdatomic.h to consider mos6502 in #if-clause
* Update gbdk-lib/libc/_divulong.c to consider mos6502 in #if-clause
* Add mos6502 to PORTS in Makefile, gbdk-lib/Makefile.common and gbdk-lib/libc/Makefile
* Update Makefile to include sdas6500 and sdld in sdcc-install rule
