Set C++11 option defaulting to 'AUTO' as it is on autotools too.

Nothing changes for already cached values.
With fresh build-dir and in 'AUTO'-mode we try to determine if the c++ compiler
is able to use this feature.

CMakeLists.txt

@@ -140,6 +140,7 @@ LYX_OPTION(ENABLE_EXPORT_TESTS "Enable for export tests" OFF ALL)
 LYX_OPTION(ASAN             "Use address sanitizer" OFF ALL)
 LYX_COMBO(USE_QT            "Use Qt version as frontend" QT4 QT5)
 LYX_OPTION(3RDPARTY_BUILD   "Build 3rdparty libs" OFF ALL)
+LYX_COMBO(ENABLE_CXX11          "Build with options for c++11-mode" AUTO ON OFF)
 
 # GCC specific
 LYX_OPTION(PROFILE              "Build profile version" OFF GCC)
@@ -149,7 +150,6 @@ LYX_OPTION(DEBUG_GLIBC          "Enable libstdc++ debug mode" OFF GCC)
 LYX_OPTION(DEBUG_GLIBC_PEDANTIC "Enable libstdc++ pedantic debug mode" OFF GCC)
 LYX_OPTION(STDLIB_DEBUG         "Use debug stdlib" OFF GCC)
 LYX_OPTION(PROFILE              "Build with options for gprof" OFF GCC)
-LYX_OPTION(ENABLE_CXX11         "Build with options for c++11-mode" OFF GCC)
 
 # MSVC specific
 LYX_OPTION(CONSOLE               "Show console on Windows, enforce with =FORCE" ON MSVC)
@@ -252,6 +252,29 @@ else()
 endif()
 
 
+if(LYX_ENABLE_CXX11 MATCHES "AUTO")
+  # Set to some meaningful default
+  find_package(CXX11Compiler)
+  if(NOT CXX11COMPILER_FOUND)
+    set(LYX_ENABLE_CXX11 OFF CACHE TYPE STRING FORCE)
+  else()
+    if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
+      execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE)
+      if(NOT GCC_VERSION VERSION_LESS 4.3)
+        set(LYX_ENABLE_CXX11 ON CACHE TYPE STRING FORCE)
+      else()
+        set(LYX_ENABLE_CXX11 OFF CACHE TYPE STRING FORCE)
+      endif()
+    else()
+      # Not a gnu compiler
+      if(CMAKE_CXX_COMPILER_ID MATCHES "^[cC]lang$")
+        set(LYX_ENABLE_CXX11 ON CACHE TYPE STRING FORCE)
+      else()
+        set(LYX_ENABLE_CXX11 OFF CACHE TYPE STRING FORCE)
+      endif()
+    endif()
+  endif()
+endif()
 set(LYX_GCC11_MODE)
 if(UNIX OR MINGW)
 	execute_process(COMMAND ${CMAKE_CXX_COMPILER} -dumpversion OUTPUT_VARIABLE GCC_VERSION OUTPUT_STRIP_TRAILING_WHITESPACE)

development/cmake/scripts/xmingw

@@ -106,7 +106,7 @@ cmake $lyxsrcdir \
     -DLYX_XMINGW=$compiler \
     -DLYX_USE_QT=QT5 \
     -DLYX_QUIET=1 \
-    -DLYX_ENABLE_CXX11=1 \
+    -DLYX_ENABLE_CXX11=ON \
     -DLYX_HUNSPELL=1 \
     -DLYX_3RDPARTY_BUILD=1 \
     $pch $mergefile