Fix unary minus to trap on overflow with -ftrapv, refactoring binop
code so we can use it from VisitUnaryMinus.

llvm-svn: 106957

Implement support for -fwrapv, rdar://7221421

As part of this, pull together trapv handling into the same enum.

This also add support for NSW multiplies.

This also makes PCH disagreement on overfl

Implement support for -fwrapv, rdar://7221421

As part of this, pull together trapv handling into the same enum.

This also add support for NSW multiplies.

This also makes PCH disagreement on overflow behavior silent, since it
really doesn't matter except for warnings and codegen (no macros get
defined etc).

llvm-svn: 106956

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