proc: move AllGCache to a common struct

Add a new method "Common" to proc.Process that returns a pointer to a
struct that pkg/proc can use to store its things, independently of the
backend.

This is used here to replace the AllGCache typecasts, it will also be
used to store the return values of the stepout breakpoint and the state
for injected function calls.

pkg/proc/interface.go

@@ -62,6 +62,8 @@ type Info interface {
 	ResumeNotify(chan<- struct{})
 	Exited() bool
 	BinInfo() *BinaryInfo
+	// Common returns a struct with fields common to all backends
+	Common() *CommonProcess
 
 	ThreadInfo
 	GoroutineInfo
@@ -100,3 +102,11 @@ type BreakpointManipulation interface {
 	ClearBreakpoint(addr uint64) (*Breakpoint, error)
 	ClearInternalBreakpoints() error
 }
+
+type CommonProcess struct {
+	allGCache []*G
+}
+
+func (p *CommonProcess) ClearAllGCache() {
+	p.allGCache = nil
+}