[Vxl-maintainers] default clang vxl build has tons of warnings

[Bill H. <bil...@ki...>]

The default build of vxl with clang produces tons of warnings like this:

/.../vxl/core/vnl/vnl_math.h:96:36: warning: in-class initializer for 
static data member of type 'const double' is a GNU extension [-Wgnu]

   static VNL_DLL_DATA const double one_over_sqrt2pi 
VCL_STATIC_CONST_INIT_FLOAT_DECL(0.39894228040143267794);


The clang vxl dashboard gets around this issue with this:
http://open.cdash.org/viewNotes.php?buildid=2820316
-Werror=gnu

This means that any gnu extensions are errors and when cmake does the 
try compile for this it will fail.   I am thinking the try compile needs 
to be fixed or maybe this usage should just be removed since it is a gnu 
only extension...

Thoughts?

-Bill