* Update gbdk_build_and_package.yml and gbdk_build_examples.yml to use gbdk-4.2.0-Next SDCC build
* Update nes.h to declare all gbdk functions with the new __no_overlay_locals function attribute
* Introduce new dedicated 16-byte overlay segment GBDKOVR, and make all assembly functions use this instead of OSEG
* Update LCC file targets.c to reserve space for both OSEG and GBDKOVR
Changes to gbdk-lib/include library headers:
* Make NONBANKED / BANKED macros in asm/mos6502/types.h expand to respective keywords instead of being no-ops
* Remove force-zero-bank version of INCBIN macros in gbdk/incbin.h in favour of regular version
* Make BANK / BANKREF macros in nes/nes.h use appropriate implementation instead of stubs
* Add SWITCH_ROM_UNROM macro, and make SWITCH_ROM use it in place of SWITCH_ROM_DUMMY in nes.h
* Add stubbed no-op versions for SWITCH_RAM / ENABLE_RAM / DISABLE_RAM in nes.h, to support cross-platform tests
changes to gbdk-support tools:
* Remove CODEFIXED segment at 0xE000 in lcc/targets.c, relying only on _CODE at 0xC000
* Make ld command use -a nes, to use virtual address translation from sdld_virtual_address_translation.patch
* Update bankpack to support "nes" as option (uses GB platform)
* Update makebin to perform NES specific bank fix (rotates ROM by one bank, putting first bank as last)
* Update png2asset to initialize bank to -1 and write #pragma bank for banks = 0, to remove assumption on bank 0 being the fixed bank
Changes to gbdk-lib/libc implementations:
* Add implementation of to_far_ptr and call__banked in targets/mos6502/far_ptr.s
* Add UNROM bank switching macros in targets/mos6502/nes/mapper_macros.s, and __swith_prg0 function in targets/mos6502/nes/mapper.s
* Add banked call support routine ___sdcc_bcall in targets/mos6502/nes/sdcc_bcall.s
* Add code to initialize switchable bank to 0 at reset in crt0
Depends on sdcc_mos6502_underscored_areas.patch, sdcc_mos6502_bank_support.patch and sdld_virtual_address_translation.patch applied to SDCC
* 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
