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.

builder/sizes.go

@@ -490,7 +490,7 @@ func loadProgramSize(path string, packagePathMap map[string]string) (*programSiz
 				continue
 			}
 			if section.Type == elf.SHT_NOBITS {
-				if section.Name == ".stack" {
+				if strings.HasPrefix(section.Name, ".stack") {
 					// TinyGo emits stack sections on microcontroller using the
 					// ".stack" name.
 					// This is a bit ugly, but I don't think there is a way to