Fix MacOS missing symbol __ZNSt3__113basic_ostreamIcNS_11char_traitsIcEEElsEi.

This is triggered by emitting operator<< 'class std::__1::basic_ostream<char,
struct std::__1::char_traits<char> > &(int)' even though its marked as exported
in general. Now that clang and libc++ agree on the handling of exported
templates we can remove our work-around.

build/unix/makeonepcm.sh

@@ -61,7 +61,7 @@ if [ ! -x core/utils/src/rootcling_tmp ]; then
   exit 0
 fi
 
-cxxflags="-D_LIBCPP_EXTERN_TEMPLATE(...)= -D__CLING__ -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -Iinclude -Ietc -Ietc/cling `cat cppflags.txt | sort | uniq`"
+cxxflags="-D__CLING__ -D__STDC_LIMIT_MACROS -D__STDC_CONSTANT_MACROS -Iinclude -Ietc -Ietc/cling `cat cppflags.txt | sort | uniq`"
 rm cppflags.txt
 
 # generate one large pcm

interpreter/cling/include/cling/Interpreter/RuntimeUniverse.h

@@ -23,11 +23,6 @@
 
 #ifdef __cplusplus
 
-#ifdef _LIBCPP_EXTERN_TEMPLATE
-#undef _LIBCPP_EXTERN_TEMPLATE
-#endif
-#define _LIBCPP_EXTERN_TEMPLATE(...)
-
 #include "cling/Interpreter/RuntimeException.h"
 
 namespace cling {