Minidump: Use minidump constants defined in llvm

This patch begins the process of migrating the "minidump" plugin to the
minidump parser in llvm. The llvm parser is not fully finished yet, but
even now, a lot of things can be switched over. The gradual migration
process will allow us to easier detect if things break than doing a big
one-step migration. Doing it early will allow us to make sure that the
llvm parser fits the use case that we need in lldb.

In this patch I start with the various minidump constants, which have
their llvm equivalent. It doesn't contain any functional changes. The
diff just reflects the different naming of things in llvm.

llvm-svn: 356898