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/panic.go

@@ -2,7 +2,7 @@ package runtime
 
 // trap is a compiler hint that this function cannot be executed. It is
 // translated into either a trap instruction or a call to abort().
-//go:export llvm.trap
+//export llvm.trap
 func trap()
 
 // Builtin function panic(msg), used as a compiler intrinsic.