Fixes for Apple Silicon

- Use -stdlib++-isystem for atdna
- Remove unnecessary constexpr from simd_neon

atdna/atdnaConfig.cmake.in

@@ -57,8 +57,8 @@ function(atdna out)
       message(FATAL_ERROR "CMAKE_OSX_SYSROOT not set")
     endif()
     list(APPEND extraargs
-         -I ${COMPILER_DIR}/../include/c++/v1
-         -isysroot ${CMAKE_OSX_SYSROOT})
+         -isysroot ${CMAKE_OSX_SYSROOT}
+         -stdlib++-isystem "${COMPILER_DIR}/../include/c++/v1")
   endif()
 
   # Make target

atdna/atdnaHelpers.cmake

@@ -108,8 +108,8 @@ function(atdna out incdirs cdefs)
       message(FATAL_ERROR "CMAKE_OSX_SYSROOT not set")
     endif()
     list(APPEND extraargs
-         -I ${COMPILER_DIR}/../include/c++/v1
-         -isysroot ${CMAKE_OSX_SYSROOT})
+         -isysroot ${CMAKE_OSX_SYSROOT}
+         -stdlib++-isystem "${COMPILER_DIR}/../include/c++/v1")
   endif()
 
   # Make target

atdna/main.cpp

@@ -51,6 +51,8 @@ static llvm::cl::list<std::string> IncludeSearchPaths("I", llvm::cl::desc("Heade
 
 static llvm::cl::list<std::string> SystemIncludeSearchPaths("isystem", llvm::cl::desc("System Header search path"));
 
+static llvm::cl::list<std::string> StandardCXXLibISystem("stdlib++-isystem", llvm::cl::desc("Standard C++ library search path"));
+
 static llvm::cl::opt<std::string> StandardCXXLib("stdlib", llvm::cl::desc("Standard C++ library"));
 
 static llvm::cl::opt<bool> DepFile("MD", llvm::cl::desc("Make Dependency file"));

include/athena/simd/simd_neon.hpp

@@ -18,7 +18,7 @@ class __simd_storage<float, m128_abi> {
 public:
   using storage_type = float32x4_t;
   storage_type __storage_{};
-  [[nodiscard]] constexpr float __get(size_t __index) const noexcept { return __storage_[__index]; }
+  [[nodiscard]] float __get(size_t __index) const noexcept { return __storage_[__index]; }
   inline void __set(size_t __index, float __val) noexcept { __storage_[__index] = __val; }
   constexpr __simd_storage(float a, float b, float c, float d) : __storage_{a, b, c, d} {}
   constexpr void __set4(float a, float b, float c, float d) noexcept { __storage_ = storage_type{a, b, c, d}; }