Bug 445235

+++ This bug was initially created as a clone of Bug #445184 +++

Valgrind has code to demangle symbols for: C++, Rust, Java, Ada, and D. But the Java/Ada/D demangling is probably broken because the code is unreachable.

`VG_(demangle)` has an initial test that requires that the first two chars be "_Z" or "_R", which excludes a bunch of cases. Also, the code in `ML_(cplus_demangle)` that calls the demanglers for Java/Ada/D is a bit different to that for C++ and Rust (in the way the `*_DEMANGLING` constants are used), which may also be a problem.

From a quick look at the code, I think the following is true.
- C++ symbols usually start with "_Z", but "_GLOBAL_" is also possible, which won't work.
- Rust symbols start with "_Z" or "_R".
- Java symbols are a subset of C++ symbols, so should be ok, modulo possible "_GLOBAL_" cases, and possible AUTO_DEMANGLING problems.
- D symbols start with "_D", and so will be broken.
- Ada symbols can start with "_ada_", or with a lower-case letter, and so will be broken.