[X86] Use C+11 non-static data member initialization to initialize all the X86 feature controls. NFC
[X86] Use C+11 non-static data member initialization to initialize all the X86 feature controls. NFC

This simplifies the constructor initialization list and makes it less likely a feature flag will be forgotten there.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@250348 91177308-0d34-0410-b5e6-96231b3b80d8

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