arm: automatically determine stack sizes

This is a big change that will determine the stack size for many
goroutines automatically. Functions that aren't recursive and don't call
function pointers can in many cases have an automatically determined
worst case stack size. This is useful, as the stack size is usually much
lower than the previous hardcoded default of 1024 bytes: somewhere
around 200-500 bytes is common.

A side effect of this change is that the default stack sizes (including
the stack size for other architectures such as AVR) can now be changed
in the config JSON file, making it tunable per application.

src/device/arm/cortexm.s

@@ -1,9 +1,11 @@
 .syntax unified
+.cfi_sections .debug_frame
 
 .section .text.HardFault_Handler
 .global  HardFault_Handler
 .type    HardFault_Handler, %function
 HardFault_Handler:
+    .cfi_startproc
     // Put the old stack pointer in the first argument, for easy debugging. This
     // is especially useful on Cortex-M0, which supports far fewer debug
     // facilities.
@@ -19,6 +21,7 @@ HardFault_Handler:
 
     // Continue handling this error in Go.
     bl handleHardFault
+    .cfi_endproc
 .size HardFault_Handler, .-HardFault_Handler
 
 // This is a convenience function for semihosting support.
@@ -27,5 +30,8 @@ HardFault_Handler:
 .global  SemihostingCall
 .type    SemihostingCall, %function
 SemihostingCall:
+    .cfi_startproc
     bkpt 0xab
     bx   lr
+    .cfi_endproc
+.size SemihostingCall, .-SemihostingCall