Make it possible to link against libstdc++ as well as libsupc++ with CMake.

Linking against libstdc++, rather than libsupc++, is probably better
for people who need to link against clients of libstdc++.  Because
libsupc++ is provided only as a static library, its globals are not
shared between the static library and the copy linked into libstdc++.
This has been found to cause at least one test failure.

This also removes a number of symbols which were multiply defined
between libstdc++ and libc++, only when linking with libstdc++.

Differential Revision: http://llvm-reviews.chandlerc.com/D1825

llvm-svn: 192075

libcxx/src/stdexcept.cpp

@@ -127,7 +127,7 @@ logic_error::operator=(const logic_error& le) _NOEXCEPT
     return *this;
 }
 
-#ifndef _LIBCPPABI_VERSION
+#if !defined(_LIBCPPABI_VERSION) && !defined(LIBSTDCXX)
 
 logic_error::~logic_error() _NOEXCEPT
 {
@@ -171,7 +171,7 @@ runtime_error::operator=(const runtime_error& le) _NOEXCEPT
     return *this;
 }
 
-#ifndef _LIBCPPABI_VERSION
+#if !defined(_LIBCPPABI_VERSION) && !defined(LIBSTDCXX)
 
 runtime_error::~runtime_error() _NOEXCEPT
 {