[LyX/master] Cmake build: Adapt use of c++11 for cygwin too.

[Kornel Benko]

commit 8c3dbe19b6cec6e465966ddf73e170984abc20f3
Author: Kornel Benko <kor...@lyx.org>
Date:   Wed Sep 9 14:45:55 2015 +0200

    Cmake build: Adapt use of c++11 for cygwin too.
    
    Change done according to commit 864a4db26bfa7ec05de936e9446d29bf8e58fc58

diff --git a/development/cmake/modules/FindCXX11Compiler.cmake 
b/development/cmake/modules/FindCXX11Compiler.cmake
index 01d5dc1..7d09f8f 100644
--- a/development/cmake/modules/FindCXX11Compiler.cmake
+++ b/development/cmake/modules/FindCXX11Compiler.cmake
@@ -37,11 +37,15 @@ INCLUDE(FindPackageHandleStandardArgs)
 if (CMAKE_CXX_COMPILER_ID MATCHES "^[cC]lang$")
   set(CXX11_FLAG_CANDIDATES "--std=c++11 -Wno-deprecated-register")
 else()
-  set(CXX11_FLAG_CANDIDATES
-    "--std=c++11"
-    "--std=gnu++11"
-    "--std=gnu++0x"
-  )
+  if (CYGWIN)
+    set(CXX11_FLAG_CANDIDATES "--std=gnu++11")
+  else()
+    set(CXX11_FLAG_CANDIDATES
+      "--std=c++11"
+      "--std=gnu++11"
+      "--std=gnu++0x"
+    )
+  endif()
 endif()
 
 # sample openmp source code to test