Avoid some unused variable warnings.

GPU/Common/VertexDecoderArm.cpp

@@ -185,6 +185,9 @@ JittedVertexDecoder VertexDecoderJitCache::Compile(const VertexDecoder &dec, int
 		}
 	}
 
+	// Not used below, but useful for logging.
+	(void)skinning;
+
 	SetCC(CC_AL);
 
 	PUSH(6, R4, R5, R6, R7, R8, R_LR);

GPU/Common/VertexDecoderArm64.cpp

@@ -165,6 +165,9 @@ JittedVertexDecoder VertexDecoderJitCache::Compile(const VertexDecoder &dec, int
 		}
 	}
 
+	// Not used below, but useful for logging.
+	(void)skinning;
+
 	// if (skinning) log = true;
 
 	BitSet32 regs_to_save(Arm64Gen::ALL_CALLEE_SAVED);

UI/BackgroundAudio.cpp

@@ -56,6 +56,10 @@ public:
 				raw_bytes_per_frame_ = temp & 0xFFFF;
 				Nothing = temp >> 16;
 
+				// Not currently used, but part of the format.
+				(void)avgBytesPerSec;
+				(void)Nothing;
+
 				if (codec == PSP_CODEC_AT3) {
 					// The first two bytes are actually not a useful part of the extradata.
 					// We already read 16 bytes, so make sure there's enough left.