Revert "Only import constructors marked noexcept."

This reverts commit 29650d8.

As discussed here, we want to import all constructors (whether they are
marked `noexcept` or not) as non-throwing initializers;

https://forums.swift.org/t/handling-c-exceptions/34823/50

Author: martinboehme

lib/ClangImporter/ImportDecl.cpp

@@ -3893,12 +3893,7 @@ namespace {
 
       AbstractFunctionDecl *result = nullptr;
       if (auto *ctordecl = dyn_cast<clang::CXXConstructorDecl>(decl)) {
-        // For the time being, we only import `noexcept` constructors.
-        // TODO: Import throwing constructors too.
-        auto *prototype = decl->getType()->getAs<clang::FunctionProtoType>();
-        if (!prototype || !prototype->hasNoexceptExceptionSpec())
-          return nullptr;
-
+        // TODO: Is failable, throws etc. correct?
         DeclName ctorName(Impl.SwiftContext, DeclBaseName::createConstructor(),
                           bodyParams);
         result = Impl.createDeclWithClangNode<ConstructorDecl>(

test/CXXInterop/Inputs/cxx_constructors.h

@@ -1,5 +1,5 @@
 struct ExplicitDefaultConstructor {
-  ExplicitDefaultConstructor() noexcept : x(42) {}
+  ExplicitDefaultConstructor() : x(42) {}
   int x;
 };
 
@@ -17,10 +17,6 @@ struct DefaultConstructorDeleted {
 };
 
 struct ConstructorWithParam {
-  ConstructorWithParam(int val) noexcept : x(val) {}
+  ConstructorWithParam(int val) : x(val) {}
   int x;
 };
-
-struct PotentiallyThrowingConstructor {
-  PotentiallyThrowingConstructor() {}
-};

test/CXXInterop/cxx-constructors-typecheck.swift

@@ -11,6 +11,3 @@ let deletedImplicitly = ConstructorWithParam() // expected-error {{missing argum
 let deletedExplicitly = DefaultConstructorDeleted() // expected-error {{cannot be constructed because it has no accessible initializers}}
 
 let withArg = ConstructorWithParam(42)
-
-// For the time being, we only import constructors marked `noexcept`.
-let potentiallyThrowing = PotentiallyThrowingConstructor() // expected-error {{cannot be constructed because it has no accessible initializers}}