Support interrupts for different platforms

Currently only C64/6502 is properly supported with interrupts.

Make a solution allowing for platform-specific / CPU-specific interrupt support.

• Support Platform ROM ISR's: The system ROM ISR addresses are different on different platforms.
• Support Different CPU's features: 65C02+ has PHX/PHY, ...

Design

• The default interrupt type is specified in the platform .TGT-file under tag "interrupt"
• The default interrupt type can be overridden using #pragma interrupt(type)
• An interrupt function can be declared using the default type by adding __interrupt
• An interrupt function can be declared using a specific type by adding __interrupt(type)
• if the type name contains the word "clobber" then the compiler calculates exactly which registers are clobbered by the interrupt procedure and replaces "clobber" with "none"/"cloba"/"clobx"/"clobax"/"clob..."/"all" depending on which registers are clobbered.
• The interrupt entry and exit ASM is generated through the ASM fragment system choosing the best ASM for the current CPU. The fragment names are
  • isr_type_entry (where type is the interrupt type name)
  • isr_type_exit (where type is the interrupt type name)

The built-in interrupt types are:

• rom_sys_c64 / rom_sys_vic20 / rom_sys_cx16: Enters through ROM. Exits through the ROM with the system ISR code (scanning keyboard, showing cursor etc.)
• rom_min_c64 / rom_min_vic20 / rom_min_cx16: Enters through ROM. Exits through the ROM with minimal code (jumps to stack pulls)
• hardware_all: Enters and exits by saving and restoring all registers.
• hardware_none: Enters and exits by saving and restoring no registers.
• hardware_clobber: Enters and exits by saving and restoring the clobbered registers.