[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/any.cpp b/src/any.cpp
index 0cf0906..415d23b 100644
--- a/src/any.cpp
+++ b/src/any.cpp
@@ -9,7 +9,7 @@
 #include "any"
 
 namespace std {
-const char* bad_any_cast::what() const _NOEXCEPT {
+const char* bad_any_cast::what() const noexcept {
     return "bad any cast";
 }
 }
@@ -24,10 +24,10 @@
 class _LIBCPP_EXCEPTION_ABI _LIBCPP_AVAILABILITY_BAD_ANY_CAST bad_any_cast : public bad_cast
 {
 public:
-    virtual const char* what() const _NOEXCEPT;
+    virtual const char* what() const noexcept;
 };
 
-const char* bad_any_cast::what() const _NOEXCEPT {
+const char* bad_any_cast::what() const noexcept {
     return "bad any cast";
 }