Merge topic 'update-for-CMake-v3.15'

eebd104 Adding a missing include(CheckSymbolExists) so that CMake 3.15 can be used

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: Ben Boeckel <ben.boeckel@kitware.com>
Merge-request: !5767

Common/Core/CMakeLists.txt

@@ -437,6 +437,8 @@ check_cxx_expression_compiles("std::isnan(0.0)" "cmath" VTK_HAS_STD_ISNAN)
 check_cxx_expression_compiles("std::isinf(0.0)" "cmath" VTK_HAS_STD_ISINF)
 check_cxx_expression_compiles("std::isfinite(0.0)" "cmath" VTK_HAS_STD_ISFINITE)
 
+include(CheckSymbolExists)
+
 # Check C99 <math.h> next, where the C99 standard says these must be.
 # (they will be found even if they are defined as macros)
 check_symbol_exists(isnan "math.h" VTK_HAS_ISNAN)