QMake: fix GCC 9 -Wdeprecated-copy warnings

Cherry-pick of efa183309e69f317189ef06fb1f13b60da9d7c63. Looks like it
was never cherry-picked as intended.

Change-Id: Iad959315ad374ef288f5fffd15d684efbcdc6197
Reviewed-by: Ville Voutilainen <ville.voutilainen@qt.io>

src/linguist/shared/proitems.h

@@ -67,6 +67,7 @@ class ProString {
 public:
     ProString();
     ProString(const ProString &other);
+    ProString &operator=(const ProString &) = default;
     PROITEM_EXPLICIT ProString(const QString &str);
     PROITEM_EXPLICIT ProString(const QStringRef &str);
     PROITEM_EXPLICIT ProString(const char *str);

src/linguist/shared/qmakeparser.h

@@ -111,7 +111,6 @@ private:
 
     struct BlockScope {
         BlockScope() : start(nullptr), braceLevel(0), special(false), inBranch(false), nest(NestNone) {}
-        BlockScope(const BlockScope &other) { *this = other; }
         ushort *start; // Where this block started; store length here
         int braceLevel; // Nesting of braces in scope
         bool special; // Single-line conditionals inside loops, etc. cannot have else branches