reflect: add support for DeepEqual

The implementation has been mostly copied from the Go reference
implementation with some small changes to fit TinyGo.

Source: https://github.com/golang/go/blob/77a11c05d6a6f766c75f804ea9b8796f9a9f85a3/src/reflect/deepequal.go

In addition, this commit also contains the following:

  - A set of tests copied from the Go reflect package.
  - An increased stack size for the riscv-qemu and hifive1-qemu targets
    (because they otherwise fail to run the tests). Because these
    targets are only used for testing, this seems fine to me.

src/reflect/value.go

@@ -140,10 +140,7 @@ func (v Value) IsNil() bool {
 func (v Value) Pointer() uintptr {
 	switch v.Kind() {
 	case Chan, Map, Ptr, UnsafePointer:
-		if v.isIndirect() {
-			return *(*uintptr)(v.value)
-		}
-		return uintptr(v.value)
+		return uintptr(v.pointer())
 	case Slice:
 		slice := (*sliceHeader)(v.value)
 		return uintptr(slice.data)
@@ -154,6 +151,15 @@ func (v Value) Pointer() uintptr {
 	}
 }
 
+// pointer returns the underlying pointer represented by v.
+// v.Kind() must be Ptr, Map, Chan, or UnsafePointer
+func (v Value) pointer() unsafe.Pointer {
+	if v.isIndirect() {
+		return *(*unsafe.Pointer)(v.value)
+	}
+	return v.value
+}
+
 func (v Value) IsValid() bool {
 	return v.typecode != 0
 }