CMake: restore NOTREACHED, without the macro-mess

- gcc (up to at least version 10) is worse at recognizing that all
  cases have been handled, so it complains about all the switches
  that cover enum values.

src/calamares/CalamaresWindow.cpp

@@ -271,6 +271,7 @@ flavoredWidget( Calamares::Branding::PanelFlavor flavor,
     case Calamares::Branding::PanelFlavor::None:
         return nullptr;
     }
+    __builtin_unreachable();
 }
 
 /** @brief Adds widgets to @p layout if they belong on this @p side

src/libcalamares/partition/PartitionSize.cpp

@@ -139,6 +139,7 @@ PartitionSize::toBytes( qint64 totalSectors, qint64 sectorSize ) const
     case SizeUnit::GiB:
         return toBytes();
     }
+    __builtin_unreachable();
 }
 
 qint64
@@ -175,7 +176,7 @@ PartitionSize::toBytes( qint64 totalBytes ) const
     case SizeUnit::GiB:
         return toBytes();
     }
-
+    __builtin_unreachable();
 }
 
 qint64
@@ -206,6 +207,7 @@ PartitionSize::toBytes() const
     case SizeUnit::GiB:
         return CalamaresUtils::GiBtoBytes( static_cast< unsigned long long >( value() ) );
     }
+    __builtin_unreachable();
 }
 
 bool
@@ -231,6 +233,7 @@ PartitionSize::operator<( const PartitionSize& other ) const
     case SizeUnit::GiB:
         return ( toBytes() < other.toBytes() );
     }
+    __builtin_unreachable();
 }
 
 bool
@@ -256,6 +259,7 @@ PartitionSize::operator>( const PartitionSize& other ) const
     case SizeUnit::GiB:
         return ( toBytes() > other.toBytes() );
     }
+    __builtin_unreachable();
 }
 
 bool
@@ -281,6 +285,7 @@ PartitionSize::operator==( const PartitionSize& other ) const
     case SizeUnit::GiB:
         return ( toBytes() == other.toBytes() );
     }
+    __builtin_unreachable();
 }
 
 }  // namespace Partition

src/libcalamares/utils/Yaml.cpp

@@ -52,6 +52,7 @@ yamlToVariant( const YAML::Node& node )
     case YAML::NodeType::Undefined:
         return QVariant();
     }
+    __builtin_unreachable();
 }
 
 

src/modules/netinstall/Config.cpp

@@ -43,6 +43,7 @@ Config::status() const
     case Status::FailedNetworkError:
         return tr( "Network Installation. (Disabled: Unable to fetch package lists, check your network connection)" );
     }
+    __builtin_unreachable();
 }
 
 

src/modules/packagechooser/PackageChooserViewStep.cpp

@@ -110,6 +110,7 @@ PackageChooserViewStep::isNextEnabled() const
         // exactly one OR one or more
         return m_widget->hasSelection();
     }
+    __builtin_unreachable();
 }