__cxa_demangle: use default member initialization
__cxa_demangle: use default member initialization

Sink the Db initialization into the structure rather than out-of-line at the
declaration size.  This just makes it easier to see what initialization is being
performed.  NFC.

git-svn-id: 6a9f6578bdee8d959f0ed58970538b4ab6004734@287364 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi,llvm-mirror/libcxxabi