Type in the LLVM IR may have names but only for the purpose of human
readability (see discussions in https://reviews.llvm.org/D40567,
In the case when the resulting IR is not proposed for reading, for
instance, when compilation produces machine code, the type names are waste
of memory. In some cases, when types are nested in other types, the memory
expenses may be really large.
This change implements new clang option, '--ir-type-names=', which controls
if IR types should be given human readable names. The option may have
values 'use' or 'none', which turn names on or off correspondently. If no such
option was specified, compiler assign names when output may be read by a
human, namely when IR is saved beyond compilation or in debug builds.