bug #1752: disable some is_convertible tests for recent compilers.

test/meta.cpp

diff --git a/test/meta.cpp b/test/meta.cpp
index ea9607f..51395ac 100644
--- a/test/meta.cpp
+++ b/test/meta.cpp
@@ -101,6 +101,14 @@
     VERIFY(( check_is_convertible(A*B, A) ));
   }
 
+  #if (EIGEN_COMP_GNUC  && EIGEN_COMP_GNUC  <=  99) \
+   || (EIGEN_COMP_CLANG && EIGEN_COMP_CLANG <= 909) \
+   || (EIGEN_COMP_MSVC  && EIGEN_COMP_MSVC  <=1914)
+  // See http://eigen.tuxfamily.org/bz/show_bug.cgi?id=1752,
+  // basically, a fix in the c++ standard breaks our c++98 implementation
+  // of is_convertible for abstract classes.
+  // So the following tests are expected to fail with recent compilers.
+
   STATIC_CHECK(( !internal::is_convertible<MyInterface, MyImpl>::value ));
   #if (!EIGEN_COMP_GNUC_STRICT) || (EIGEN_GNUC_AT_LEAST(4,8))
   // GCC prior to 4.8 fails to compile this test:
@@ -110,12 +118,16 @@
   STATIC_CHECK(( !internal::is_convertible<MyImpl, MyInterface>::value ));
   #endif
   STATIC_CHECK((  internal::is_convertible<MyImpl, const MyInterface&>::value ));
+
+  #endif
+
   {
     int i;
     VERIFY(( check_is_convertible(fix<3>(), i) ));
     VERIFY((!check_is_convertible(i, fix<DynamicIndex>()) ));
   }
 
+
   VERIFY((  internal::has_ReturnType<FooReturnType>::value ));
   VERIFY((  internal::has_ReturnType<ScalarBinaryOpTraits<int,int> >::value ));
   VERIFY(( !internal::has_ReturnType<MatrixXf>::value ));