Fix downstream review comments for C++20

This CL addresses the review comments for
https://webrtc-review.googlesource.com/c/src/+/261221
in the downstream cherry-pick: https://crrev.com/c/4660950.

*   Always use size_t{} for casting.
*   Remove unneeded size_t casts.
*   Avoid using __x as it is reserved for the compiler.

Bug: b:217226507
Change-Id: I13c57cb69d7db066ac9a6dbd15b7f6de54abb613
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/311360
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Li-Yu Yu <aaronyu@google.com>
Cr-Commit-Position: refs/heads/main@{#40395}

modules/audio_processing/vad/vad_audio_proc.h

diff --git a/modules/audio_processing/vad/vad_audio_proc.h b/modules/audio_processing/vad/vad_audio_proc.h
index cbdd707..905c687 100644
--- a/modules/audio_processing/vad/vad_audio_proc.h
+++ b/modules/audio_processing/vad/vad_audio_proc.h
@@ -51,21 +51,19 @@
   // For every 30 ms we compute 3 spectral peak there for 3 LPC analysis.
   // LPC is computed over 15 ms of windowed audio. For every 10 ms sub-frame
   // we need 5 ms of past signal to create the input of LPC analysis.
-  static constexpr size_t kNumPastSignalSamples =
-      static_cast<size_t>(kSampleRateHz / 200);
+  static constexpr size_t kNumPastSignalSamples = size_t{kSampleRateHz / 200};
 
   // TODO(turajs): maybe defining this at a higher level (maybe enum) so that
   // all the code recognize it as "no-error."
   static constexpr int kNoError = 0;
 
   static constexpr size_t kNum10msSubframes = 3;
-  static constexpr size_t kNumSubframeSamples =
-      static_cast<size_t>(kSampleRateHz / 100);
+  static constexpr size_t kNumSubframeSamples = size_t{kSampleRateHz / 100};
   // Samples in 30 ms @ given sampling rate.
   static constexpr size_t kNumSamplesToProcess =
-      size_t{kNum10msSubframes} * kNumSubframeSamples;
+      kNum10msSubframes * kNumSubframeSamples;
   static constexpr size_t kBufferLength =
-      size_t{kNumPastSignalSamples} + kNumSamplesToProcess;
+      kNumPastSignalSamples + kNumSamplesToProcess;
   static constexpr size_t kIpLength = kDftSize >> 1;
   static constexpr size_t kWLength = kDftSize >> 1;
   static constexpr size_t kLpcOrder = 16;

rtc_base/system/no_unique_address.h

diff --git a/rtc_base/system/no_unique_address.h b/rtc_base/system/no_unique_address.h
index 6bede2c..a40db34 100644
--- a/rtc_base/system/no_unique_address.h
+++ b/rtc_base/system/no_unique_address.h
@@ -25,7 +25,7 @@
 // clang-cl doesn't support it yet and support is unclear also when the target
 // platform is iOS.
 #ifndef __has_cpp_attribute
-#define __has_cpp_attribute(__x) 0
+#define __has_cpp_attribute(x) 0
 #endif
 #if __has_cpp_attribute(no_unique_address)
 // NOLINTNEXTLINE(whitespace/braces)