 - Unconditionally allow p{read,write}{,v}().
 - Unconditionally allow p{read,write}{,v}().

 - clang complains about unused values computed by C expressions

 - clang makes extensive use of SSE registers. This requires us to 
   explicitly align the stack pointer in x86-32. It seems as if x86-64
   already works correctly, but we might need to revisit this assessment
   if we encounter problems.

 - clang doesn't implicitly do a const_cast() when it does a 
   reinterpret_cast(). We now do a C-style cast instead, as that ends
   up being more readable.

 - the code should now compile with clang, but it still doesn't behave
   quite correctly. Do not use seccomp&clang in production until I commit
   the next set of changes.
Review URL: http://codereview.chromium.org/7394001

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@92722 0039d316-1c4b-4281-b951-d872f2087c98

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