Make considerably more progress on AARCH64

- Utilities like pledge.com now build
- kprintf() will no longer balk at 48-bit addresses
- There's a new aarch64-dbg build mode that should work
- gc() and defer() are mostly pacified; avoid using them on aarch64
- THIRD_PART_STB now has Arm Neon intrinsics for fast image handling

build/config.mk

@@ -130,6 +130,12 @@ TARGET_ARCH ?= -msse3
 OVERRIDE_CCFLAGS += -fno-pie
 endif
 
+ifeq ($(MODE), aarch64-dbg)
+CONFIG_CPPFLAGS += -DMODE_DBG
+CONFIG_CCFLAGS += $(BACKTRACES) $(FTRACE) -DSYSDEBUG -O -fno-inline
+CONFIG_COPTS += -fsanitize=undefined
+endif
+
 # System Five Mode
 #
 #   - `make MODE=sysv`