Fix -Wunused-but-set-variable

Bug: chromium:1203071
Change-Id: I338bd31ab0e74751f2c0abd5d441ea03ac33dead
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/237880
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35350}

rtc_base/system/unused.h

@@ -18,7 +18,11 @@
 // Note: In most cases it is better to remove the unused variable rather than
 // suppressing the compiler warning.
 #ifndef RTC_UNUSED
+#ifdef __cplusplus
 #define RTC_UNUSED(x) static_cast<void>(x)
+#else
+#define RTC_UNUSED(x) (void)(x)
+#endif
 #endif  // RTC_UNUSED
 
 #endif  // RTC_BASE_SYSTEM_UNUSED_H_

sdk/BUILD.gn

@@ -1083,6 +1083,7 @@ if (is_ios || is_mac) {
             "../media:rtc_media_tests_utils",
             "../rtc_base",
             "../rtc_base:gunit_helpers",
+            "../rtc_base/system:unused",
             "../system_wrappers",
             "//third_party/libyuv",
           ]

sdk/objc/unittests/RTCPeerConnectionFactory_xctest.m

@@ -21,6 +21,7 @@
 #import "api/peerconnection/RTCRtpTransceiver.h"
 #import "api/peerconnection/RTCSessionDescription.h"
 #import "api/peerconnection/RTCVideoSource.h"
+#import "rtc_base/system/unused.h"
 
 #import <XCTest/XCTest.h>
 
@@ -64,6 +65,7 @@
       factory = nil;
     }
     mediaStream = nil;
+    RTC_UNUSED(mediaStream);
   }
 
   XCTAssertTrue(true, "Expect test does not crash");

sdk/objc/unittests/nalu_rewriter_xctest.mm

@@ -352,6 +352,7 @@ static const uint8_t SPS_PPS_BUFFER[] = {
                                               cmsampleSize,
                                               kCMBlockBufferAssureMemoryNowFlag,
                                               &block_buffer);
+  XCTAssertEqual(kCMBlockBufferNoErr, status);
 
   status = CMSampleBufferCreate(nullptr,
                                 block_buffer,
@@ -365,6 +366,7 @@ static const uint8_t SPS_PPS_BUFFER[] = {
                                 0,
                                 nullptr,
                                 &sample_buffer);
+  XCTAssertEqual(noErr, status);
 
   return sample_buffer;
 }