* Pull runtime variable 'goarmsoftfp' to detect if soft-float ABI is used.
* Assembly trampolines skips load/store to FP registers if soft-float is detected. This was implemented in exactly same way how it's done in Go runtime.
* Apply integer passing rules for float arguments/return values.
* Run tests for GOARM=5 (no FPU) in test workflow and add some arm-specific test cases.

Closes #490

Co-authored-by: Hirador <63920290+Hirador@users.noreply.github.com>