Revert "[lld] Add support for other demanglers other than Itanium"

This reverts commit e60d6dfd5acdc821d391ad5af2c706397bdfd36a.

clang-ppc64le-rhel buildbot failed (https://lab.llvm.org/buildbot#builders/57/builds/13424):

    tools/lld/MachO/CMakeFiles/lldMachO.dir/Symbols.cpp.o: In function `lld::demangle(llvm::StringRef, bool)':
    Symbols.cpp:(.text._ZN3lld8demangleEN4llvm9StringRefEb[_ZN3lld8demangleEN4llvm9StringRefEb]+0x90): undefined reference to `llvm::demangle(std::string const&)'

1 files changed, 13 insertions, 0 deletions

diff --git a/lld/Common/Strings.cpp b/lld/Common/Strings.cpp
index 6e5478e335ca..7bf336490dae 100644
--- a/lld/Common/Strings.cpp
+++ b/lld/Common/Strings.cpp
@@ -9,6 +9,7 @@
 #include "lld/Common/Strings.h"
 #include "lld/Common/ErrorHandler.h"
 #include "lld/Common/LLVM.h"
+#include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/FileSystem.h"
 #include "llvm/Support/GlobPattern.h"
 #include <algorithm>
@@ -18,6 +19,18 @@
 using namespace llvm;
 using namespace lld;
 
+// Returns the demangled C++ symbol name for name.
+std::string lld::demangleItanium(StringRef name) {
+  // demangleItanium() can be called for all symbols. Only demangle C++ symbols,
+  // to avoid getting unexpected result for a C symbol that happens to match a
+  // mangled type name such as "Pi" (which would demangle to "int*").
+  if (!name.startswith("_Z") && !name.startswith("__Z") &&
+      !name.startswith("___Z") && !name.startswith("____Z"))
+    return std::string(name);
+
+  return demangle(std::string(name));
+}
+
 SingleStringMatcher::SingleStringMatcher(StringRef Pattern) {
   if (Pattern.size() > 2 && Pattern.startswith("\"") &&
       Pattern.endswith("\"")) {