main: add -print-allocs flag that lets you print all heap allocations

This flag, if set, is a regexp for function names. If there are heap
allocations in the matching function names, these heap allocations will
be printed with an explanation why the heap allocation exists (and why
the object can't be stack allocated).

compileopts/options.go

@@ -2,6 +2,7 @@ package compileopts
 
 import (
 	"fmt"
+	"regexp"
 	"strings"
 )
 
@@ -27,6 +28,7 @@ type Options struct {
 	PrintCommands bool
 	Debug         bool
 	PrintSizes    string
+	PrintAllocs   *regexp.Regexp // regexp string
 	PrintStacks   bool
 	Tags          string
 	WasmAbi       string