[ClangImporter] Check for builtin conformance in importNumericLiteral

Make sure the destination type actually conforms to the corresponding
builtin literal protocol before attempting to import it. We may want
to consider allowing any type that conforms to the non-builtin literal
protocol, but I want to keep this patch low risk and just ensure we at
least don't crash for now.

rdar://156524292

test/ClangImporter/rdar156524292.swift

@@ -0,0 +1,28 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+// RUN: %target-swift-frontend -typecheck -verify %t/main.swift -I %t -verify-additional-file %t/cmodule.h
+
+// REQUIRES: objc_interop
+// REQUIRES: OS=macosx
+
+//--- cmodule.h
+#import <CoreGraphics/CoreGraphics.h>
+#define intLiteralCGFloat ((CGFloat)0)
+// expected-note@-1 {{invalid numeric literal}}
+// expected-note@-2 {{macro 'intLiteralCGFloat' unavailable (cannot import)}}
+#define floatLiteralCGFloat ((CGFloat)0.0)
+// expected-note@-1 {{invalid numeric literal}}
+// expected-note@-2 {{macro 'floatLiteralCGFloat' unavailable (cannot import)}}
+
+//--- module.modulemap
+module CModule [system] {
+  header "cmodule.h"
+  export *
+}
+
+//--- main.swift
+import CModule
+
+// Make sure we don't crash when attempting to import these.
+_ = intLiteralCGFloat // expected-error {{cannot find 'intLiteralCGFloat' in scope}}
+_ = floatLiteralCGFloat // expected-error {{cannot find 'floatLiteralCGFloat' in scope}}