As reported in https://github.com/ldc-developers/ldc/issues/3501#issuecomment-661551187.
Previously, LDC would simply override an existing TypeDescriptor global
with an equivalent definition if assertions were disabled.
Use different equivalent TypeDescriptors in this exotic case now, by
using proper mangling. [The linker can presumably still fold duplicates
via ICF.]
Ideally, these descriptors would be truly unique, but WinEH depends on
string comparisons to check for matching catch clauses, and currently
depends on TypeInfo_Class.name to generate these strings at runtime when
throwing an exception, see
19731a92a9/src/ldc/eh_msvc.d (L192-L211).
So if those names were fully qualified (`cd->toPrettyChars(*true*)`
during ClassInfo generation), we'd be fine, but that'd obviously be a
breaking change and diverge from upstream.
The part needing most attention was ddmd.root.ctfloat, ddmd.target (incl.
gen/target.cpp) and ddmd.builtin. The front-end is now prepared for
elaborate compile-time floating-point types to allow for proper cross-
compilation.
This version still uses the host's `real` type for compile-time reals,
except for MSVC hosts, which still use 64-bit doubles (when compiled with
DMD host compiler too).
Some other changes:
* semantic*() of Statements extracted from statement.d to statementsem.d
* mangle() -> mangleToBuffer()
* Identifier::string -> toChars()
* Token::float80value => floatvalue
* Dsymbol::isAggregateMember() => isMember()
* BoolExp is no more
* ddmd.root.ctfloat: LDC-specific CTFE builtins
Windows x64 ABI: remove unnecessary \01 from mangled symbol name.
This removes the 0x1 byte from `.mangleof` accessible from user code.
Resolves issue #1519
Also let mangleForLLVM take a std::string, to enable C++11's moves.
