Fixes to support building in -std=c++20 mode.

* Structs with user-declared constructors are no longer considered
  aggregates, so remove the declarations when possible
* Types of both arguments to "==" must match to avoid "ambiguous
  function call" warning
* Various types of math involving enums are deprecated, so replace with
  constexprs where necessary
* ABSL_CONST_INIT must be used on definition as well as declaration
* volatile memory may no longer be read from and written to by the same
  operator, so replace e.g. "n++" with "n = n + 1"
* Replace an outdated check for no_unique_address support with
  __has_cpp_attribute
* std::result_of(f(x)) has been removed, replace with
  std::invoke_result(f, x)

Bug: chromium:1284275
Change-Id: I77b366ab1da7eb2c1e4c825b2714417c31ee5903
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/261221
Auto-Submit: Peter Kasting <pkasting@chromium.org>
Reviewed-by: Tomas Gunnarsson <tommi@google.com>
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36786}

modules/audio_processing/include/aec_dump.cc

@@ -17,7 +17,7 @@ InternalAPMConfig::InternalAPMConfig(InternalAPMConfig&&) = default;
 InternalAPMConfig& InternalAPMConfig::operator=(const InternalAPMConfig&) =
     default;
 
-bool InternalAPMConfig::operator==(const InternalAPMConfig& other) {
+bool InternalAPMConfig::operator==(const InternalAPMConfig& other) const {
   return aec_enabled == other.aec_enabled &&
          aec_delay_agnostic_enabled == other.aec_delay_agnostic_enabled &&
          aec_drift_compensation_enabled ==

modules/audio_processing/include/aec_dump.h

@@ -31,7 +31,7 @@ struct InternalAPMConfig {
   InternalAPMConfig& operator=(const InternalAPMConfig&);
   InternalAPMConfig& operator=(InternalAPMConfig&&) = delete;
 
-  bool operator==(const InternalAPMConfig& other);
+  bool operator==(const InternalAPMConfig& other) const;
 
   bool aec_enabled = false;
   bool aec_delay_agnostic_enabled = false;

modules/audio_processing/utility/delay_estimator_wrapper.cc

@@ -21,8 +21,8 @@ namespace webrtc {
 
 // Only bit `kBandFirst` through bit `kBandLast` are processed and
 // `kBandFirst` - `kBandLast` must be < 32.
-enum { kBandFirst = 12 };
-enum { kBandLast = 43 };
+constexpr int kBandFirst = 12;
+constexpr int kBandLast = 43;
 
 static __inline uint32_t SetBit(uint32_t in, int pos) {
   uint32_t mask = (1 << pos);

modules/audio_processing/vad/vad_audio_proc.h

@@ -35,7 +35,7 @@ class VadAudioProc {
                       size_t length,
                       AudioFeatures* audio_features);
 
-  static const size_t kDftSize = 512;
+  static constexpr size_t kDftSize = 512;
 
  private:
   void PitchAnalysis(double* pitch_gains, double* pitch_lags_hz, size_t length);
@@ -51,28 +51,24 @@ class VadAudioProc {
   // 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.
-  enum : size_t {
-    kNumPastSignalSamples = static_cast<size_t>(kSampleRateHz / 200)
-  };
+  static constexpr size_t kNumPastSignalSamples =
+      static_cast<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."
-  enum : int { kNoError = 0 };
+  static constexpr int kNoError = 0;
 
-  enum : size_t { kNum10msSubframes = 3 };
-  enum : size_t {
-    kNumSubframeSamples = static_cast<size_t>(kSampleRateHz / 100)
-  };
-  enum : size_t {
-    // Samples in 30 ms @ given sampling rate.
-    kNumSamplesToProcess = kNum10msSubframes * kNumSubframeSamples
-  };
-  enum : size_t {
-    kBufferLength = kNumPastSignalSamples + kNumSamplesToProcess
-  };
-  enum : size_t { kIpLength = kDftSize >> 1 };
-  enum : size_t { kWLength = kDftSize >> 1 };
-  enum : size_t { kLpcOrder = 16 };
+  static constexpr size_t kNum10msSubframes = 3;
+  static constexpr size_t kNumSubframeSamples =
+      static_cast<size_t>(kSampleRateHz / 100);
+  // Samples in 30 ms @ given sampling rate.
+  static constexpr size_t kNumSamplesToProcess =
+      size_t{kNum10msSubframes} * kNumSubframeSamples;
+  static constexpr size_t kBufferLength =
+      size_t{kNumPastSignalSamples} + kNumSamplesToProcess;
+  static constexpr size_t kIpLength = kDftSize >> 1;
+  static constexpr size_t kWLength = kDftSize >> 1;
+  static constexpr size_t kLpcOrder = 16;
 
   size_t ip_[kIpLength];
   float w_fft_[kWLength];