Everywhere: Fix -Winconsistent-missing-override warnings from Clang

This option is already enabled when building Lagom, so let's enable it
for the main build too. We will no longer be surprised by Lagom Clang
CI builds failing while everything compiles locally.

Furthermore, the stronger `-Wsuggest-override` warning is enabled in
this commit, which enforces the use of the `override` keyword in all
classes, not just those which already have some methods marked as
`override`. This works with both GCC and Clang.

Kernel/FileSystem/AnonymousFile.h

@@ -24,7 +24,7 @@ public:
 
 private:
     virtual StringView class_name() const override { return "AnonymousFile"sv; }
-    virtual ErrorOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const;
+    virtual ErrorOr<NonnullOwnPtr<KString>> pseudo_path(const OpenFileDescription&) const override;
     virtual bool can_read(const OpenFileDescription&, size_t) const override { return false; }
     virtual bool can_write(const OpenFileDescription&, size_t) const override { return false; }
     virtual ErrorOr<size_t> read(OpenFileDescription&, u64, UserOrKernelBuffer&, size_t) override { return ENOTSUP; }

Kernel/FileSystem/ProcFS.h

@@ -54,8 +54,8 @@ protected:
     ProcFS const& procfs() const { return static_cast<ProcFS const&>(Inode::fs()); }
 
     // ^Inode
-    virtual ErrorOr<void> attach(OpenFileDescription& description) = 0;
-    virtual void did_seek(OpenFileDescription&, off_t) = 0;
+    virtual ErrorOr<void> attach(OpenFileDescription& description) override = 0;
+    virtual void did_seek(OpenFileDescription&, off_t) override = 0;
     virtual ErrorOr<void> flush_metadata() override final;
     virtual ErrorOr<NonnullRefPtr<Inode>> create_child(StringView name, mode_t, dev_t, UserID, GroupID) override final;
     virtual ErrorOr<void> add_child(Inode&, StringView name, mode_t) override final;

Kernel/FileSystem/SysFS.h

@@ -146,7 +146,7 @@ protected:
     virtual ErrorOr<void> chmod(mode_t) override;
     virtual ErrorOr<void> chown(UserID, GroupID) override;
     virtual ErrorOr<void> truncate(u64) override;
-    virtual ErrorOr<void> set_mtime(time_t);
+    virtual ErrorOr<void> set_mtime(time_t) override;
 
     virtual ErrorOr<void> attach(OpenFileDescription& description) override final;
     virtual void did_seek(OpenFileDescription&, off_t) override final;

Kernel/Firmware/PowerStateSwitch.h

@@ -26,7 +26,7 @@ public:
     virtual mode_t permissions() const override;
     virtual ErrorOr<size_t> write_bytes(off_t, size_t, UserOrKernelBuffer const&, OpenFileDescription*) override;
     virtual ErrorOr<void> truncate(u64) override;
-    virtual ErrorOr<void> set_mtime(time_t) { return {}; }
+    virtual ErrorOr<void> set_mtime(time_t) override { return {}; }
 
 private:
     PowerStateSwitchNode(FirmwareSysFSDirectory&);

Kernel/Graphics/GenericFramebufferDevice.h

@@ -29,7 +29,7 @@ public:
     virtual ~GenericFramebufferDevice() = default;
 
     // ^File
-    virtual ErrorOr<Memory::Region*> mmap(Process&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared) = 0;
+    virtual ErrorOr<Memory::Region*> mmap(Process&, OpenFileDescription&, Memory::VirtualRange const&, u64 offset, int prot, bool shared) override = 0;
     virtual ErrorOr<void> ioctl(OpenFileDescription&, unsigned request, Userspace<void*> arg) override final;
     virtual StringView class_name() const override final { return "FramebufferDevice"sv; }
 

Kernel/Graphics/VirtIOGPU/FramebufferDevice.h

@@ -30,8 +30,8 @@ public:
 
     virtual ErrorOr<void> try_to_initialize() override { return {}; }
 
-    virtual void deactivate_writes();
-    virtual void activate_writes();
+    virtual void deactivate_writes() override;
+    virtual void activate_writes() override;
 
     size_t width() const { return display_info().rect.width; }
     size_t height() const { return display_info().rect.height; }

Kernel/Net/NE2000NetworkAdapter.h

@@ -31,12 +31,12 @@ public:
         // just assume that it's up.
         return true;
     }
-    virtual i32 link_speed()
+    virtual i32 link_speed() override
     {
         // Can only do 10mbit..
         return 10;
     }
-    virtual bool link_full_duplex() { return true; }
+    virtual bool link_full_duplex() override { return true; }
 
     virtual StringView purpose() const override { return class_name(); }