all: change //go:export to //export

This is the kind that is used in Go (actually CGo) for exporting
functions. I think it's best to use //export instead of our custom
//go:export pragma, for consistency (they are equivalent in TinyGo).
Therefore I've updated all instances to the standard format (except for
two that are updated in https://github.com/tinygo-org/tinygo/pull/1024).

No smoke tests changed (when comparing the output hash), except for some
wasm tests that include DWARF debug info and tend to be flaky anyway.

src/runtime/runtime_cortexm.go

@@ -74,7 +74,7 @@ type interruptStack struct {
 // For details, see:
 // https://community.arm.com/developer/ip-products/system/f/embedded-forum/3257/debugging-a-cortex-m0-hard-fault
 // https://blog.feabhas.com/2013/02/developing-a-generic-hard-fault-handler-for-arm-cortex-m3cortex-m4/
-//go:export handleHardFault
+//export handleHardFault
 func handleHardFault(sp *interruptStack) {
 	print("fatal error: ")
 	if uintptr(unsafe.Pointer(sp)) < 0x20000000 {