Remove LLVM_NOEXCEPT and replace it with noexcept

Now that we have dropped MSVC 2013, all supported compilers support
noexcept and we can drop this portability macro.

llvm-svn: 284672

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -6581,7 +6581,7 @@ namespace {
 // will be removed once this transition is complete. Clients should prefer to
 // deal with the Error value directly, rather than converting to error_code.
 class BitcodeErrorCategoryType : public std::error_category {
-  const char *name() const LLVM_NOEXCEPT override {
+  const char *name() const noexcept override {
     return "llvm.bitcode";
   }
   std::string message(int IE) const override {