[LyX/master] Fix MSVC C++11 detection

[Georg Baum]

commit 3c56e7c0eb8d1d00b5783a11e69cff50e1e53790
Author: Georg Baum <b...@lyx.org>
Date:   Sat Jul 2 18:26:08 2016 +0200

    Fix MSVC C++11 detection
    
    The old version with empty flag did not enter the loop at all, so we have to
    use a workaround. Thanks Uwe for testing.
---
 development/cmake/modules/FindCXX11Compiler.cmake |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/development/cmake/modules/FindCXX11Compiler.cmake 
b/development/cmake/modules/FindCXX11Compiler.cmake
index c7045d1..5c7b698 100644
--- a/development/cmake/modules/FindCXX11Compiler.cmake
+++ b/development/cmake/modules/FindCXX11Compiler.cmake
@@ -44,7 +44,7 @@ else()
       # MSVC does not have a general C++11 flag, one can only switch off
       # MS extensions with /Za in general or by extension with /Zc.
       # Use an empty flag to ensure that CXX11_STD_REGEX is correctly set.
-      set(CXX11_FLAG_CANDIDATES "")
+      set(CXX11_FLAG_CANDIDATES "noflagneeded")
     else()
       set(CXX11_FLAG_CANDIDATES
         "--std=c++14"
@@ -113,7 +113,9 @@ set(SAFE_CMAKE_REQUIRED_QUIET ${CMAKE_REQUIRED_QUIET})
 set(CMAKE_REQUIRED_QUIET ON)
 SET(SAFE_CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS}")
 FOREACH(FLAG ${CXX11_FLAG_CANDIDATES})
-  SET(CMAKE_REQUIRED_FLAGS "${FLAG}")
+  IF(NOT "${FLAG}" STREQUAL "noflagneeded")
+    SET(CMAKE_REQUIRED_FLAGS "${FLAG}")
+  ENDIF()
   UNSET(CXX11_FLAG_DETECTED CACHE)
   CHECK_CXX_SOURCE_COMPILES("${CXX11_TEST_SOURCE}" CXX11_FLAG_DETECTED)
   IF(CXX11_FLAG_DETECTED)
@@ -136,5 +138,8 @@ set(CMAKE_REQUIRED_QUIET ${SAFE_CMAKE_REQUIRED_QUIET})
 
 # handle the standard arguments for find_package
 FIND_PACKAGE_HANDLE_STANDARD_ARGS(CXX11Compiler DEFAULT_MSG CXX11_FLAG)
+IF("${CXX11_FLAG}" STREQUAL "noflagneeded")
+  SET(CXX11_FLAG "")
+ENDIF()
 
 MARK_AS_ADVANCED(CXX11_FLAG CXX11_STD_REGEX)