Bump cortex-m-rt to get access to _stack_end symbol

[korken89]

No description provided.

[mciantyre]

imxrt-rt users are expected to override the cortex-m-rt linker script. With this in mind, how will users see that _stack_end symbol?

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imxrt-rt uses a fixed stack size, and we have symbols for the start and end of the stack. Could we expose __estack through a Rust API, similar to heap_end()? That could give users a clear way to access the address.

imxrt-rt/src/host/imxrt-link.x

Lines 40 to 47 in ca26336

	.stack (NOLOAD) : ALIGN(8)
	{
	__estack = .;
	. += ALIGN(__stack_size, 8);
	__sstack = .;
	/* Symbol expected by cortex-m-rt */
	_stack_start = __sstack;
	} > REGION_STACK

[korken89]

Ah sorry, I was fixing a lot of different MSPLIM related PRs and this went with the rest 😅
The thing is that we use pre-init already, I need to check how this can be used so MSPLIM is set before we call main and its stack is allocated.
I'll fix on Monday :)