Support multiple global registers

[fuzyll]

What is the feature you'd like to have?
Issue #3223 was fixed and is awesome. Unfortunately, we currently only support a single global register value. It would be awesome if we could support multiple.

Is your feature request related to a problem?
Sometimes, you just have more than one, y'know?

Are any alternative solutions acceptable?
None that I can think of.

Additional Information:
You can hack around this with UIDF already, but it's less-than-ideal.

[emesare]

An example of an architecture that would benefit from this is tricore.

2.2.1.4 System Global Registers
Address registers A[0], A[1], A[8], and A[9] are designated as system global registers.
They are not part of either context partition and are not saved/restored across calls. They
can be protected against write access by user applications.

https://www.infineon.com/dgdl/TriCore_EABI_v2_3.pdf?fileId=db3a304412b407950112b40f8d7a142b

[alexmullins]

PowerPC is another arch that would benefit from this. The EABI specifies R2 and R13 be used as global pointers to data sections.

https://www.nxp.com/docs/en/application-note/PPCEABI.pdf