🐛 Fix _exit implementation

[ion098]

Summary:

Changes the _exit function to flush the serial buffer and indefinitely block.

Motivation:

The _exit function is supposed to never return, but right now it does.

Test Plan:

• Check it compiles
• Test that _exit exits the code
• Test that _exit always flushes the serial buffer

Test Code:

printf("hi");
std::exit(0);
asm volatile("mov r0, #0 \n\tSTR sp, [r0]\n\t"); // if exit does not immediately, there will be a data abort

[WillXuCodes]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[WillXuCodes]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[BennyBot]

@ion098 did you test this already?

[ion098]

@ion098 did you test this already?

No, I haven't been able to test this yet.

[ion098]

@Rocky14683 This should be ready for hardware testing, can you rerun the pipeline?

[Rocky14683]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[AndrewLuGit]

https://artprodcus3.artifacts.visualstudio.com/A268c8aad-3bb0-47d2-9a57-cf06a843d2e8/a421d041-2579-4bf8-a0aa-d7a0307dade3/_apis/artifact/cGlwZWxpbmVhcnRpZmFjdDovL3B1cmR1ZS1hY20tc2lnYm90cy9wcm9qZWN0SWQvYTQyMWQwNDEtMjU3OS00YmY4LWEwYWEtZDdhMDMwN2RhZGUzL2J1aWxkSWQvNjU5OC9hcnRpZmFjdE5hbWUvdGVtcGxhdGU1/content?format=zip

[AndrewLuGit]

@ion098 using the test code you've given, it doesn't print "hi" to the terminal before exiting.

[AndrewLuGit]

👍