[asan] Keep Itanium mangled names in global metadata

The runtime calls `MaybeDemangleGlobalName` for error reporting and
`__cxxabiv1::__cxa_demangle` is called if available, so demanging Itanium
mangled names in global metadata is unnecessary and wastes data size.

Add `MaybeDemangleGlobalName` in ODR violation detection to support demangled
names in a suppressions file. `MaybeDemangleGlobalName` may call
`DemangleCXXABI` and leak memory. Use an internal allocation to prevent lsan
leak (in case there is no fatal asan error).

The debug feature `report_globals=2` prints information for all instrumented
global variables. `MaybeDemangleGlobalName` would be slow, so don't do that.
The output looks like `Added Global[0x56448f092d60]: beg=0x56448fa66d60 size=4/32 name=_ZL13test_global_2`
and I think the mangled name is fine.

Other mangled schemes e.g. Windows (see win-string-literal.ll) remain the
current behavior.

Reviewed By: hctim

Differential Revision: https://reviews.llvm.org/D138095