[embedded] Fix 3 compilation warnings in embedded stdlib

Author: kubamracek

stdlib/public/core/EmbeddedPrint.swift

@@ -36,7 +36,7 @@ public func print(_ string: StaticString, terminator: StaticString = "\n") {
 @_disfavoredOverload
 public func print(_ string: String, terminator: StaticString = "\n") {
   var string = string
-  _ = string.withUTF8 { buf in
+  string.withUTF8 { buf in
     for c in buf {
       putchar(CInt(c))
     }
@@ -51,7 +51,7 @@ public func print(_ string: String, terminator: StaticString = "\n") {
 @_disfavoredOverload
 public func print(_ object: some CustomStringConvertible, terminator: StaticString = "\n") {
   var string = object.description
-  _ = string.withUTF8 { buf in
+  string.withUTF8 { buf in
     for c in buf {
       putchar(CInt(c))
     }

stdlib/public/core/Optional.swift

@@ -437,6 +437,7 @@ extension Optional: CustomDebugStringConvertible {
       #if !$Embedded
       debugPrint(value, terminator: "", to: &result)
       #else
+      _ = value
       "(cannot print value in embedded Swift)".write(to: &result)
       #endif
       result += ")"