Fix build with older (<3.0) swigs
Fix build with older (<3.0) swigs

It turns out it wasn't the compilers, but swig who had issues with my
previous patch -- older versions do not recognise the "constexpr"
keyword.

Fortunately, that can be fixed the same way we fix all other swig
incompatibilities: #ifndef SWIG.

git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@349153 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb