[libc++/abi] Replace uses of _NOEXCEPT in src/ by noexcept

We always build the libraries in a Standard mode that supports noexcept,
so there's no need to use the _NOEXCEPT macro.

Differential Revision: https://reviews.llvm.org/D97700

GitOrigin-RevId: 5601305fb30bf585c397e62d2d3a8a712e47d70b
diff --git a/src/stdlib_exception.cpp b/src/stdlib_exception.cpp
index b0cc431..5f9e643 100644
--- a/src/stdlib_exception.cpp
+++ b/src/stdlib_exception.cpp
@@ -14,22 +14,22 @@
 
 // exception
 
-exception::~exception() _NOEXCEPT
+exception::~exception() noexcept
 {
 }
 
-const char* exception::what() const _NOEXCEPT
+const char* exception::what() const noexcept
 {
   return "std::exception";
 }
 
 // bad_exception
 
-bad_exception::~bad_exception() _NOEXCEPT
+bad_exception::~bad_exception() noexcept
 {
 }
 
-const char* bad_exception::what() const _NOEXCEPT
+const char* bad_exception::what() const noexcept
 {
   return "std::bad_exception";
 }
@@ -37,32 +37,32 @@
 
 //  bad_alloc
 
-bad_alloc::bad_alloc() _NOEXCEPT
+bad_alloc::bad_alloc() noexcept
 {
 }
 
-bad_alloc::~bad_alloc() _NOEXCEPT
+bad_alloc::~bad_alloc() noexcept
 {
 }
 
 const char*
-bad_alloc::what() const _NOEXCEPT
+bad_alloc::what() const noexcept
 {
     return "std::bad_alloc";
 }
 
 // bad_array_new_length
 
-bad_array_new_length::bad_array_new_length() _NOEXCEPT
+bad_array_new_length::bad_array_new_length() noexcept
 {
 }
 
-bad_array_new_length::~bad_array_new_length() _NOEXCEPT
+bad_array_new_length::~bad_array_new_length() noexcept
 {
 }
 
 const char*
-bad_array_new_length::what() const _NOEXCEPT
+bad_array_new_length::what() const noexcept
 {
     return "bad_array_new_length";
 }