Only use .CPP .CXX and .C++ do not work by default with g+++.

Modules/CMakeCXXCompiler.cmake.in

@@ -22,7 +22,7 @@ IF(CMAKE_COMPILER_IS_MINGW)
 ENDIF(CMAKE_COMPILER_IS_MINGW)
 SET(CMAKE_CXX_COMPILER_ID_RUN 1)
 SET(CMAKE_CXX_IGNORE_EXTENSIONS inl;h;hpp;HPP;H;o;O;obj;OBJ;def;DEF;rc;RC)
-SET(CMAKE_CXX_SOURCE_FILE_EXTENSIONS C;M;c++;cc;cpp;cxx;m;mm;C++;CC;CPP;CXX)
+SET(CMAKE_CXX_SOURCE_FILE_EXTENSIONS C;M;c++;cc;cpp;cxx;m;mm;CPP)
 SET(CMAKE_CXX_LINKER_PREFERENCE 30)
 SET(CMAKE_CXX_LINKER_PREFERENCE_PROPAGATES 1)
 

Tests/CxxOnly/CMakeLists.txt

@@ -2,7 +2,7 @@
 project (CxxOnly CXX)
 
 set(CMAKE_DEBUG_POSTFIX "_test_debug_postfix")
-add_library(testcxx1 STATIC libcxx1.cxx test.CPP test.CXX test.C++)
+add_library(testcxx1 STATIC libcxx1.cxx test.CPP)
 add_library(testcxx2 SHARED libcxx2.cxx)
 add_executable (CxxOnly cxxonly.cxx)
 target_link_libraries(CxxOnly testcxx1 testcxx2)

Tests/CxxOnly/cxxonly.cxx

@@ -1,14 +1,12 @@
 #include "libcxx1.h"
 #include "libcxx2.h"
 extern int testCPP;
-extern int testCXX;
-extern int testCplusplus;
 
 #include <stdio.h>
 
 int main ()
 {
-  testCPP = testCXX= testCplusplus = 1;
+  testCPP = 1;
   if ( LibCxx1Class::Method() != 2.0 )
     {
     printf("Problem with libcxx1\n");

Tests/CxxOnly/test.C++

@@ -1 +0,0 @@
-int testCplusplus;

Tests/CxxOnly/test.CXX

@@ -1 +0,0 @@
-int testCXX;