* improve the ZIR generated of variable decls
- utilize the same ZIR for the type and init value when possible
- init value gets a result location with the variable type.
no manual coercion is required.
* no longer use return instructions to extract values out of comptime
blocks. Instead run the analysis and then look at the corresponding
analyzed instruction, relying on the comptime mechanism to report
errors when something could not be comptime evaluated.
* move SPU code from std to self hosted compiler
* change std lib comments to be descriptive rather than prescriptive
* avoid usingnamespace
* fix case style of error codes
* remove duplication of producer_string
* generalize handling of less than 64 bit arch pointers
* clean up SPU II related test harness code
