Fix -Wunused-but-set-variable.

This is part of a set of CLs to fix the Chromium roll.

Bug: None
Change-Id: I7cc1e5b84a2443f311fb4e047954d7d4d9c41189
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/236761
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35284}

rtc_tools/sanitizers_unittest.cc

@@ -55,6 +55,7 @@ TEST(SanitizersDeathTest, AddressSanitizer) {
 void SignedIntegerOverflow() {
   int32_t x = 1234567890;
   x *= 2;
+  (void)x;
 }
 
 // For ubsan_vptr:

system_wrappers/source/cpu_features_linux.cc

@@ -66,6 +66,7 @@ uint64_t GetCPUFeaturesARM(void) {
   }
 #endif  // WEBRTC_GLIBC_PREREQ(2, 16)
 #if defined(__aarch64__)
+  (void)platform;
   architecture = 8;
   if ((hwcap & HWCAP_FP) != 0)
     result |= kCPUFeatureVFPv3;