More subtle checking for redeclarations:

More subtle checking for redeclarations:
 - 300 doesn't allow built-in overload, while 100 does, while neither allows redefining
 - block name can't be reused for block name within the same interface
   (though, the spec. isn't clear about that, it's easier than verifying member matches, will file bug on it)

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@23984 e7fa87d3-cd2b-0410-9028-fcbf551c1848