If you pass `-ExtName` to the `--spirv-ext` command line option. that
should disable the extension. However some vendors have some extensions
enabled by default when using a triple with that vendor, and disabling
an extension with the option did not effect the default extensions.
This PR makes it so disabling an extension with the `--spirv-ext` option
actually disables the extension.
The problem was we only considered the disabled extension when parsing
the arguments for `--spirv-ext`, but the default extensions are added
separately, so we need to store the disabled extensions and factor them
in when computing the final extension set to use.
Signed-off-by: Nick Sarnie <nick.sarnie@intel.com>
78689630b3