common: Make use of [[nodiscard]] where applicable

Now that clang-format makes [[nodiscard]] attributes format sensibly, we
can apply them to several functions within the common library to allow
the compiler to complain about any misuses of the functions.

src/common/wall_clock.h

@@ -14,24 +14,24 @@ namespace Common {
 class WallClock {
 public:
     /// Returns current wall time in nanoseconds
-    virtual std::chrono::nanoseconds GetTimeNS() = 0;
+    [[nodiscard]] virtual std::chrono::nanoseconds GetTimeNS() = 0;
 
     /// Returns current wall time in microseconds
-    virtual std::chrono::microseconds GetTimeUS() = 0;
+    [[nodiscard]] virtual std::chrono::microseconds GetTimeUS() = 0;
 
     /// Returns current wall time in milliseconds
-    virtual std::chrono::milliseconds GetTimeMS() = 0;
+    [[nodiscard]] virtual std::chrono::milliseconds GetTimeMS() = 0;
 
     /// Returns current wall time in emulated clock cycles
-    virtual u64 GetClockCycles() = 0;
+    [[nodiscard]] virtual u64 GetClockCycles() = 0;
 
     /// Returns current wall time in emulated cpu cycles
-    virtual u64 GetCPUCycles() = 0;
+    [[nodiscard]] virtual u64 GetCPUCycles() = 0;
 
     virtual void Pause(bool is_paused) = 0;
 
     /// Tells if the wall clock, uses the host CPU's hardware clock
-    bool IsNative() const {
+    [[nodiscard]] bool IsNative() const {
         return is_native;
     }
 
@@ -47,7 +47,7 @@ private:
     bool is_native;
 };
 
-std::unique_ptr<WallClock> CreateBestMatchingClock(u32 emulated_cpu_frequency,
-                                                   u32 emulated_clock_frequency);
+[[nodiscard]] std::unique_ptr<WallClock> CreateBestMatchingClock(u32 emulated_cpu_frequency,
+                                                                 u32 emulated_clock_frequency);
 
 } // namespace Common