[patch] libstdc++/64571 export fstream functions using new std::string

[Jonathan Wakely]

The existing tests for these functions are compile-only so didn't
catch that I forgot to export these new symbols. I'll add a better
test next week.

Tested x86_64-linux, committed to trunk.

commit d428e75af04d995451a917ef7c9caed6b8cee737
Author: Jonathan Wakely <jwak...@redhat.com>
Date:   Tue Jan 13 14:27:34 2015 +0000

    	PR libstdc++/64571
    	* config/abi/pre/gnu.ver: Export fstream functions using new string.

diff --git a/libstdc++-v3/config/abi/pre/gnu.ver b/libstdc++-v3/config/abi/pre/gnu.ver
index 7bb65e9..700da18 100644
--- a/libstdc++-v3/config/abi/pre/gnu.ver
+++ b/libstdc++-v3/config/abi/pre/gnu.ver
@@ -1648,6 +1648,13 @@ GLIBCXX_3.4.21 {
     _ZStlsI[cw]St11char_traitsI[cw]ESaI[cw]EERSt13basic_ostreamIT_T0_ES7_RKNSt7__cxx1112basic_string*;
     _ZStrsI[cw]St11char_traitsI[cw]ESaI[cw]EERSt13basic_istreamIT_T0_ES7_RNSt7__cxx1112basic_string*;
 
+    # fstream functions taking ABI-tagged std::string
+    _ZNSt13basic_filebufI[cw]St11char_traitsI[cw]EE4openERKNSt7__cxx1112basic_string*;
+    _ZNSt13basic_fstreamI[cw]St11char_traitsI[cw]EEC1ERKNSt7__cxx1112basic_string*;
+    _ZNSt13basic_fstreamI[cw]St11char_traitsI[cw]EE4openERKNSt7__cxx1112basic_string*;
+    _ZNSt14basic_[io]fstreamI[cw]St11char_traitsI[cw]EEC1ERKNSt7__cxx1112basic_string*;
+    _ZNSt14basic_[io]fstreamI[cw]St11char_traitsI[cw]EE4openERKNSt7__cxx1112basic_string*;
+
     # std::locale::name() returning new std::string
     _ZNKSt6locale4nameB5cxx11Ev;