all: add support for multicore scheduler

This commit adds support for a scheduler that runs a scheduler on all
available cores. It is meant to be used on baremetal systems with a
fixed number of cores, such as the RP2040.

The initial implementation adds support for multicore scheduling to the
riscv-qemu target as a convenient testing target. This means that this
new multicore scheduler is tested in CI, including a bunch of standard
library tests (`make tinygo-test-baremetal`). This should ensure the new
scheduler is reasonably well tested before trying to use it on
harder-to-debug targets like the RP2040.

src/runtime/panic.go

@@ -99,7 +99,8 @@ func runtimePanicAt(addr unsafe.Pointer, msg string) {
 	} else {
 		printstring("panic: runtime error: ")
 	}
-	println(msg)
+	printstring(msg)
+	printnl()
 	abort()
 }