[NFC] Rename _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS

The name _LIBCPP_TYPE_VIS_ONLY is no longer accurate because both
_LIBCPP_TYPE_VIS and _LIBCPP_TYPE_VIS_ONLY expand to
__attribute__((__type_visibility__)) with Clang. The only remaining difference
is that _LIBCPP_TYPE_VIS_ONLY can be applied to templates whereas
_LIBCPP_TYPE_VIS cannot (due to dllimport/dllexport not being allowed on
templates).

This patch renames _LIBCPP_TYPE_VIS_ONLY to _LIBCPP_TEMPLATE_VIS.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@291035 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/string b/include/string
index 98f538c..136a5fb 100644
--- a/include/string
+++ b/include/string
@@ -497,7 +497,7 @@
 // fpos
 
 template <class _StateT>
-class _LIBCPP_TYPE_VIS_ONLY fpos
+class _LIBCPP_TEMPLATE_VIS fpos
 {
 private:
     _StateT __st_;
@@ -555,7 +555,7 @@
 operator+(const basic_string<_CharT, _Traits, _Allocator>& __x, _CharT __y);
 
 template <bool>
-class _LIBCPP_TYPE_VIS_ONLY __basic_string_common
+class _LIBCPP_TEMPLATE_VIS __basic_string_common
 {
 protected:
     _LIBCPP_NORETURN void __throw_length_error() const;
@@ -630,7 +630,7 @@
 #endif  // _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
 
 template<class _CharT, class _Traits, class _Allocator>
-class _LIBCPP_TYPE_VIS_ONLY basic_string
+class _LIBCPP_TEMPLATE_VIS basic_string
     : private __basic_string_common<true>
 {
 public:
@@ -3870,7 +3870,7 @@
                    basic_string<_CharT, _Traits, _Allocator>::npos;
 
 template<class _CharT, class _Traits, class _Allocator>
-struct _LIBCPP_TYPE_VIS_ONLY hash<basic_string<_CharT, _Traits, _Allocator> >
+struct _LIBCPP_TEMPLATE_VIS hash<basic_string<_CharT, _Traits, _Allocator> >
     : public unary_function<basic_string<_CharT, _Traits, _Allocator>, size_t>
 {
     size_t