Fixed buffer overflow in demangler

Changing the name of ErrorProtocol to Error broke this runtime test —
causing a buffer overflow.

The mangled name changed from _TtPs13ErrorProtocol_->_TtPs5Error_  but
the strlen didn’t change from 21 to 12; I update the callers to use
static string length instead of a literal string & length.

Error reported is:
=================================================================
==88865==ERROR: AddressSanitizer: global-buffer-overflow on address
0x0001028ba40d at pc 0x000103291a1f bp 0x7fff5d3492c0 sp 0x7fff5d348a80
READ of size 9 at 0x0001028ba40d thread T0
(libclang_rt.asan_osx_dynamic.dylib+0x42a1e)
std::__1::char_traits<char>, std::__1::allocator<char> >::__init(char
const*, unsigned long) (libc++.1.dylib+0x3f224)
swift::Demangle::NodeFactory::create(swift::Demangle::Node::Kind,
llvm::StringRef) string:2044
namespace)::Demangler::demangleTopLevel() Demangle.cpp:358
unsigned long, swift::Demangle::DemangleOptions const&)
Demangle.cpp:2288
MetadataReader.h:772

0x0001028ba40d is located 51 bytes to the left of global variable
'<string literal>' defined in
'/Users/buildslave/jenkins/workspace/swift-incremental-asan-RDA/swift/to
ols/swift-reflection-test/swift-reflection-test.c:458:19' (0x1028ba440)
of size 41
'<string literal>' is ascii string 'swift-reflection-test <binary
filename>
'
0x0001028ba40d is located 0 bytes to the right of global variable
'<string literal>' defined in
'/Users/buildslave/jenkins/workspace/swift-incremental-asan-RDA/swift/to
ols/swift-reflection-test/swift-reflection-test.c:435:15' (0x1028ba400)
of size 13
'<string literal>' is ascii string '_TtPs5Error_'

SUMMARY: AddressSanitizer: global-buffer-overflow
(libclang_rt.asan_osx_dynamic.dylib+0x42a1e) in wrap_memmove

Author: joewillsher

tools/swift-reflection-test/swift-reflection-test.c

@@ -421,18 +421,21 @@ int doDumpHeapInstance(const char *BinaryFilename) {
             return EXIT_SUCCESS;
           break;
         case Existential: {
+          static const char Name[] = "_TtP_";
           swift_typeref_t AnyTR
-            = swift_reflection_typeRefForMangledTypeName(RC, "_TtP_", 5);
+            = swift_reflection_typeRefForMangledTypeName(RC,
+              Name, sizeof(Name)-1);
 
           printf("Reflecting an existential.\n");
           if (!reflectExistential(RC, Pipe, AnyTR))
             return EXIT_SUCCESS;
           break;
         }
         case ErrorExistential: {
+          static const char ErrorName[] = "_TtPs5Error_";
           swift_typeref_t ErrorTR
             = swift_reflection_typeRefForMangledTypeName(RC,
-              "_TtPs5Error_", 21);
+              ErrorName, sizeof(ErrorName)-1);
           printf("Reflecting an error existential.\n");
           if (!reflectExistential(RC, Pipe, ErrorTR))
             return EXIT_SUCCESS;