Simplify ClFlags macro for older C++ standards.
Simplify ClFlags macro for older C++ standards.

Visual Studio 2015 does not support the use of typename outside of a
template definition. Instead alias the flag's storage type. This
even avoids some duplication.

BUG=swiftshader:7

Change-Id: I787701f6bfe8e36169e6ac5d63fcb6a1a114bdb0

bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader