Fix build with GNU libstdc++ C++11 ABI

The GNU libstdc++ that ships witch gcc 5 can be used with the same ABI as
older versions, or with a new ABI which is conformant to the C++11 standard.
LyX did not build if the latter was used:
https://kojipkgs.fedoraproject.org//work/tasks/1267/9651267/build.log

This is now fixed by detecting the ABI version and disabling the wrong forward
declarations. At the same time, STD_STRING_USES_COW is switched off for the
C++11 ABI version, because the std::basic_string implementation is now C++11
conformant. Since the GNU libstdc++ can also used by other compilers such as
clang, we must not test for the compiler version.

config/lyxinclude.m4

@@ -120,37 +120,65 @@ done
 ])dnl
 
 
-AC_DEFUN([LYX_PROG_CXX_WORKS],
-[rm -f conftest.C
-cat >conftest.C <<EOF
-class foo {
-   // we require the mutable keyword
-   mutable int bar;
- };
- // we require namespace support
- namespace baz {
-   int bar;
- }
- int main() {
-   return(0);
- }
-EOF
-$CXX -c $CXXFLAGS $CPPFLAGS conftest.C >&5 || CXX=
-rm -f conftest.C conftest.o conftest.obj || true
+dnl Usage: LYX_PROG_CLANG: set lyx_cv_prog_clang to yes if the compiler is clang.
+AC_DEFUN([LYX_PROG_CLANG],
+[AC_CACHE_CHECK([whether the compiler is clang],
+               [lyx_cv_prog_clang],
+[AC_TRY_COMPILE([], [
+#ifndef __clang__
+	    this is not clang
+#endif
+],
+[lyx_cv_prog_clang=yes ; CLANG=yes], [lyx_cv_prog_clang=no ; CLANG=no])])
+])
+
+
+dnl Usage: LYX_LIB_STDCXX: set lyx_cv_lib_stdcxx to yes if the STL library is libstdc++.
+AC_DEFUN([LYX_LIB_STDCXX],
+[AC_CACHE_CHECK([whether STL is libstdc++],
+               [lyx_cv_lib_stdcxx],
+[AC_TRY_COMPILE([#include<vector>], [
+#if ! defined(__GLIBCXX__) && ! defined(__GLIBCPP__)
+	    this is not libstdc++
+#endif
+],
+[lyx_cv_lib_stdcxx=yes], [lyx_cv_lib_stdcxx=no])])
+])
+
+
+dnl Usage: LYX_LIB_STDCXX_CXX11_ABI: set lyx_cv_lib_stdcxx_cxx11_abi to yes
+dnl        if the STL library is GNU libstdc++ and the C++11 ABI is used.
+AC_DEFUN([LYX_LIB_STDCXX_CXX11_ABI],
+[AC_CACHE_CHECK([whether STL is libstdc++ using the C++11 ABI],
+               [lyx_cv_lib_stdcxx_cxx11_abi],
+[AC_TRY_COMPILE([#include<vector>], [
+#if ! defined(_GLIBCXX_USE_CXX11_ABI) || ! _GLIBCXX_USE_CXX11_ABI
+	    this is not libstdc++ using the C++11 ABI
+#endif
+],
+[lyx_cv_lib_stdcxx_cxx11_abi=yes], [lyx_cv_lib_stdcxx_cxx11_abi=no])])
 ])
 
 
 AC_DEFUN([LYX_PROG_CXX],
-[AC_MSG_CHECKING([for a good enough C++ compiler])
-LYX_SEARCH_PROG(CXX, $CXX $CCC g++ gcc c++ CC cxx xlC cc++, [LYX_PROG_CXX_WORKS])
+[AC_REQUIRE([AC_PROG_CXX])
+AC_REQUIRE([AC_PROG_CXXCPP])
 
-if test -z "$CXX" ; then
-  AC_MSG_ERROR([Unable to find a good enough C++ compiler])
+AC_LANG_PUSH(C++)
+LYX_PROG_CLANG
+LYX_LIB_STDCXX
+LYX_LIB_STDCXX_CXX11_ABI
+AC_LANG_POP(C++)
+
+if test $lyx_cv_lib_stdcxx = "yes" ; then
+  if test $lyx_cv_lib_stdcxx_cxx11_abi = "yes" ; then
+    AC_DEFINE(USE_GLIBCXX_CXX11_ABI, 1, [use GNU libstdc++ with C++11 ABI])
+  fi
+else
+  if test $lyx_cv_prog_clang = "yes" ; then
+    AC_DEFINE(USE_LLVM_LIBCPP, 1, [use libc++ provided by llvm instead of GNU libstdc++])
+  fi
 fi
-AC_MSG_RESULT($CXX)
-
-AC_PROG_CXX
-AC_PROG_CXXCPP
 
 ### We might want to get or shut warnings.
 AC_ARG_ENABLE(warnings,

development/cmake/ConfigureChecks.cmake

@@ -112,3 +112,49 @@ check_cxx_source_compiles(
 	"
 SIZEOF_WCHAR_T_IS_4)
 
+# Check whether STL is libstdc++
+check_cxx_source_compiles(
+	"
+	#include <vector>
+	int main() {
+	#if ! defined(__GLIBCXX__) && ! defined(__GLIBCPP__)
+		this is not libstdc++
+	#endif
+		return(0);
+	}
+	"
+lyx_cv_lib_stdcxx)
+
+# Check whether STL is libstdc++ with C++11 ABI
+check_cxx_source_compiles(
+	"
+	#include <vector>
+	int main() {
+	#if ! defined(_GLIBCXX_USE_CXX11_ABI) || ! _GLIBCXX_USE_CXX11_ABI
+		this is not libstdc++ using the C++11 ABI
+	#endif
+		return(0);
+	}
+	"
+USE_GLIBCXX_CXX11_ABI)
+
+check_cxx_source_compiles(
+	"
+	#ifndef __clang__
+		this is not clang
+	#endif
+	int main() {
+	  return(0);
+	}
+	"
+lyx_cv_prog_clang)
+
+set(USE_LLVM_LIBCPP)
+set(USE_GLIBCXX_CXX11_ABI)
+if(NOT lyx_cv_lib_stdcxx)
+  if(lyx_cv_prog_clang)
+    # use libc++ provided by llvm instead of GNU libstdc++
+    set(USE_LLVM_LIBCPP 1)
+  endif()
+endif()
+

development/cmake/config.h.cmake

@@ -57,6 +57,9 @@
 #cmakedefine LYX_USE_TR1 1
 #cmakedefine LYX_USE_TR1_REGEX 1
 
+// use GNU libstdc++ with C++11 ABI
+#cmakedefine USE_GLIBCXX_CXX11_ABI 1
+
 #cmakedefine Z_PREFIX 1
 
 #cmakedefine ASPELL_FOUND 1

src/support/strfwd.h

@@ -13,14 +13,6 @@
 #ifndef STRFWD_H
 #define STRFWD_H
 
-// This includes does nothing but defining _LIBCPP_VERSION
-// if libc++ is used (rather than libstdc++) - we first
-// check if we have at least a c++03 standard before
-// including the file
-#if (__cplusplus > 19971L)
-#include <ciso646>
-#endif
-
 #ifdef USE_WCHAR_T
 
 // Prefer this if possible because GNU libstdc++ has usable
@@ -36,8 +28,10 @@ namespace lyx { typedef boost::uint32_t char_type; }
 
 #endif
 
-// Forward definitions do not work with libc++
-#ifdef  _LIBCPP_VERSION
+// For gcc5 with the new std::string ABI forward declarations would work in
+// principle, but I am not sure whether we want non-standard
+// "namespace __cxx11" in our sources.
+#if defined(USE_LLVM_LIBCPP) || defined(USE_GLIBCXX_CXX11_ABI)
 #include <string>
 #else
 

status.21x

@@ -231,3 +231,6 @@ What's new
 - Add "Keywords" to lyx.desktop file (bug 9414).
 
 - Fix several compilation warnings (bug 9488).
+
+- Fix build with gcc 5.1 using libstdc++ with C++11 ABI.
+