mesa/extensions: Enable overriding permanently enabled extensions
mesa/extensions: Enable overriding permanently enabled extensions

Provide the ability to prevent any permanently enabled extension
from appearing in the string returned by glGetString[i]().

Signed-off-by: Nanley Chery <d78cd5d33e98a5581566f188959f731bd0b1c0fd@intel.com>
Reviewed-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>
Tested-by: Brian Paul <3cb4e1df5ec4da2c7c4af7c52cec8cf340a55a10@vmware.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler