[Support] Fix AlignOf test on i386-linux.
[Support] Fix AlignOf test on i386-linux.

On i386 alignof(double) = 8 is not the same as alignof(struct { double
}) = 4. This used to be not an issue because the old implementation
always measured alignment inside of structs. Wrap a dummy struct around
the test to avoid this issue.

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@284812 91177308-0d34-0410-b5e6-96231b3b80d8

GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,apple/swift-llvm,llvm-mirror/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm