NORSPEC-49 Add shader profiler, add support for ARB_depth_clamp where available

indra/llrender/llgl.cpp

indra/llrender/llgl.h

indra/llrender/llglheaders.h

indra/llrender/llglslshader.cpp

indra/llrender/llglslshader.h

indra/llrender/llvertexbuffer.cpp

...p_settings/shaders/class1/deferred/attachmentShadowV.glsl

...w/app_settings/shaders/class1/deferred/avatarShadowF.glsl

...w/app_settings/shaders/class1/deferred/avatarShadowV.glsl

...app_settings/shaders/class1/deferred/diffuseIndexedF.glsl

...ewview/app_settings/shaders/class1/deferred/diffuseV.glsl

...pp_settings/shaders/class1/deferred/shadowAlphaMaskF.glsl

...pp_settings/shaders/class1/deferred/shadowAlphaMaskV.glsl

...iew/app_settings/shaders/class1/deferred/shadowCubeV.glsl

...newview/app_settings/shaders/class1/deferred/shadowF.glsl

...newview/app_settings/shaders/class1/deferred/shadowV.glsl

indra/newview/llspatialpartition.cpp

indra/newview/llviewerdisplay.cpp

indra/newview/llviewermenu.cpp

indra/newview/llviewershadermgr.cpp