[OpenCL 2.0] Enable program scope variables, Section 6.5.1.

 - Remove virtual SC_OpenCLWorkGroupLocal storage type specifier
as it conflicts with static local variables now and prevents
diagnosing static local address space variables correctly.

 - Allow static local and global variables (OpenCL2.0 s6.8 and s6.5.1).

 - Improve diagnostics of allowed ASes for variables in different scopes:
(i) Global or static local variables have to be in global
or constant ASes (OpenCL1.2 s6.5, OpenCL2.0 s6.5.1);
(ii) Non-kernel function variables can't be declared in local
or constant ASes (OpenCL1.1 s6.5.2 and s6.5.3).

http://reviews.llvm.org/D13105

llvm-svn: 248906