Fix errors when building in C++20 mode (#4528)

 * use [[noreturn]] available since C++11 instead of compiler-specific attributes
 * replace deprecated std::is_pod with is_trivial&&is_standard_layout (also available since C++11/14)
 * explicitly capture this in [=] lambdas
 * extra const functions in FeatureSet, fix implicit cast warning by using the features field directly
 * Use CMAKE_CXX_STANDARD to ensure the C++ standard parameter is set on all targets, remove manual compiler flag workaround.

2 files changed, 11 insertions, 9 deletions

diff --git a/src/support/utilities.cpp b/src/support/utilities.cpp
index ea426df9c..f051a1871 100644
--- a/src/support/utilities.cpp
+++ b/src/support/utilities.cpp
@@ -24,9 +24,8 @@
 #include "sanitizer/common_interface_defs.h"
 #endif
 
-void wasm::handle_unreachable(const char* msg,
-                              const char* file,
-                              unsigned line) {
+[[noreturn]] void
+wasm::handle_unreachable(const char* msg, const char* file, unsigned line) {
 #ifndef NDEBUG
   if (msg) {
     std::cerr << msg << "\n";
diff --git a/src/support/utilities.h b/src/support/utilities.h
index 38fe6fd73..57d170269 100644
--- a/src/support/utilities.h
+++ b/src/support/utilities.h
@@ -36,8 +36,11 @@ template<class Destination, class Source>
 inline Destination bit_cast(const Source& source) {
   static_assert(sizeof(Destination) == sizeof(Source),
                 "bit_cast needs to be between types of the same size");
-  static_assert(std::is_pod<Destination>::value, "non-POD bit_cast undefined");
-  static_assert(std::is_pod<Source>::value, "non-POD bit_cast undefined");
+  static_assert(std::is_trivial_v<Destination> &&
+                  std::is_standard_layout_v<Destination>,
+                "non-POD bit_cast undefined");
+  static_assert(std::is_trivial_v<Source> && std::is_standard_layout_v<Source>,
+                "non-POD bit_cast undefined");
   Destination destination;
   std::memcpy(&destination, &source, sizeof(destination));
   return destination;
@@ -65,7 +68,7 @@ public:
     std::cerr << arg;
     return *this;
   }
-  WASM_NORETURN ~Fatal() {
+  [[noreturn]] ~Fatal() {
     std::cerr << "\n";
     // Use _Exit here to avoid calling static destructors. This avoids deadlocks
     // in (for example) the thread worker pool, where workers hold a lock while
@@ -74,9 +77,9 @@ public:
   }
 };
 
-WASM_NORETURN void handle_unreachable(const char* msg = nullptr,
-                                      const char* file = nullptr,
-                                      unsigned line = 0);
+[[noreturn]] void handle_unreachable(const char* msg = nullptr,
+                                     const char* file = nullptr,
+                                     unsigned line = 0);
 
 // If control flow reaches the point of the WASM_UNREACHABLE(), the program is
 // undefined.