SmallString: Fix ambiguity of iterators

std::size_t is a undefined unsigned integer type and std::ptrdiff_t is a
undefined signed integer type. So sometimes the compiler doesn't know
which to choose because both could represent a integer.

Change-Id: I669cd44c6f16854dfe3f3cc44edbfc422e1cbd6a
Reviewed-by: Tim Jenssen <tim.jenssen@theqtcompany.com>

src/libs/utils/smallstring.h

@@ -267,12 +267,12 @@ public:
 
     reverse_iterator rbegin() noexcept
     {
-        return reverse_iterator(end() - 1l);
+        return reverse_iterator(end() - static_cast<std::size_t>(1));
     }
 
     reverse_iterator rend() noexcept
     {
-        return reverse_iterator(begin() - 1l);
+        return reverse_iterator(begin() - static_cast<std::size_t>(1));
     }
 
     const_iterator begin() const noexcept

src/libs/utils/smallstringliteral.h

@@ -90,12 +90,12 @@ public:
 
     const_reverse_iterator rbegin() const noexcept
     {
-        return const_reverse_iterator(end() - 1l);
+        return const_reverse_iterator(end() - static_cast<std::size_t>(1));
     }
 
     const_reverse_iterator rend() const noexcept
     {
-        return const_reverse_iterator(begin() - 1l);
+        return const_reverse_iterator(begin() - static_cast<std::size_t>(1));
     }
 
     constexpr static

src/libs/utils/smallstringview.h

@@ -106,12 +106,12 @@ public:
 
     const_reverse_iterator rbegin() const noexcept
     {
-        return const_reverse_iterator(end() - 1l);
+        return const_reverse_iterator(end() - static_cast<std::size_t>(1));
     }
 
     const_reverse_iterator rend() const noexcept
     {
-        return const_reverse_iterator(begin() - 1l);
+        return const_reverse_iterator(begin() - static_cast<std::size_t>(1));
     }
 
 private: