[clang][DeclPrinter] Fix printing for noexcept expressions

[kadircet]

Summary

We are already building into the final result, no need to append it
again.

Fixes https://github.com/clangd/vscode-clangd/issues/290.

[kbobyrev]

LG, thanks!

clang/lib/AST/DeclPrinter.cpp

if (const FunctionType *AFT = Ty->getAs<FunctionType>()) {
     } else if (FT && isNoexceptExceptionSpec(FT->getExceptionSpecType())) {
       Proto += " noexcept";
       if (isComputedNoexcept(FT->getExceptionSpecType())) {
         Proto += "(";
         llvm::raw_string_ostream EOut(Proto);
         FT->getNoexceptExpr()->printPretty(EOut, nullptr, SubPolicy,
                                            Indentation, "\n", &Context);
         EOut.flush();
-        Proto += EOut.str();
         Proto += ")";
       }
     }
 
     if (CDecl) {
       if (!Policy.TerseOutput)
         PrintConstructorInitializers(CDecl, Proto);
     } else if (!ConversionDecl && !isa<CXXDestructorDecl>(D)) {

clang/unittests/AST/DeclPrinterTest.cpp

 }
 
 TEST(DeclPrinter, TestFunctionDecl_ExceptionSpecification5) {
   ASSERT_TRUE(PrintedDeclCXX11Matches(
     "struct Z {"
     "  void A(int a) noexcept(true);"
     "};",
     "A",
-    "void A(int a) noexcept(trueA(int a) noexcept(true)"));
-    // WRONG; Should be: "void A(int a) noexcept(true);"
+    "void A(int a) noexcept(true)"));
 }
 
 TEST(DeclPrinter, TestFunctionDecl_ExceptionSpecification6) {
   ASSERT_TRUE(PrintedDeclCXX11Matches(
     "struct Z {"
     "  void A(int a) noexcept(1 < 2);"
     "};",
     "A",
-    "void A(int a) noexcept(1 < 2A(int a) noexcept(1 < 2)"));
-    // WRONG; Should be: "void A(int a) noexcept(1 < 2);"
+    "void A(int a) noexcept(1 < 2)"));
 }
 
 TEST(DeclPrinter, TestFunctionDecl_ExceptionSpecification7) {
   ASSERT_TRUE(PrintedDeclCXX11Matches(
     "template<int N>"
     "struct Z {"
     "  void A(int a) noexcept(N < 2);"
     "};",
     "A",
-    "void A(int a) noexcept(N < 2A(int a) noexcept(N < 2)"));
-    // WRONG; Should be: "void A(int a) noexcept(N < 2);"
+    "void A(int a) noexcept(N < 2)"));
 }
 
 TEST(DeclPrinter, TestVarDecl1) {
   ASSERT_TRUE(PrintedDeclCXX98Matches(
     "char *const (*(*A)[5])(int);",
     "A",
     "char *const (*(*A)[5])(int)"));
     // Should be: with semicolon