Revert "Turn off extern templates for most uses."

Turning off explicit template instantiation leads to a pretty
significant build time and code size cost. We're better off dealing
with ABI incompatibility issues that come up in a less heavy handed
way.

This reverts commit r189610.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@215740 91177308-0d34-0410-b5e6-96231b3b80d8

include/__config

@@ -608,7 +608,7 @@ template <unsigned> struct __static_assert_check {};
 #endif
 
 #ifndef _LIBCPP_EXTERN_TEMPLATE
-#define _LIBCPP_EXTERN_TEMPLATE(...)
+#define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
 #endif
 
 #ifndef _LIBCPP_EXTERN_TEMPLATE2

src/algorithm.cpp

@@ -7,7 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
 #include "algorithm"
 #include "random"
 #include "mutex"

src/ios.cpp

@@ -7,8 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
-
 #include "ios"
 #include "streambuf"
 #include "istream"

src/locale.cpp

@@ -7,8 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
-
 // On Solaris, we need to define something to make the C99 parts of localeconv
 // visible.
 #ifdef __sun__

src/string.cpp

@@ -7,8 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
-
 #include "string"
 #include "cstdlib"
 #include "cwchar"

src/valarray.cpp

@@ -7,8 +7,6 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define _LIBCPP_EXTERN_TEMPLATE(...) extern template __VA_ARGS__;
-
 #include "valarray"
 
 _LIBCPP_BEGIN_NAMESPACE_STD