The logic in 509be7cf1f10c5d329d2b0524f2af6bfcabd52de assumed that
`use_llvm` meant that the LLVM backend would be used, however, use_llvm
is false when there are no zig files to compile, which is the case for
zig cc. This logic resulted in `-fsingle-threaded` which made libc++
fail to compile for C++ code that includes the threading abstractions
(such as LLVM).
Perform these transformations in this priority order:
1. If the `else` expression is missing or an empty block, replace the condition with `if (true)` if it is not already.
2. If the `then` block is empty, replace the condition with `if (false)` if it is not already.
3. If the condition is `if (true)`, replace the `if` expression with the contents of the `then` expression.
4. If the condition is `if (false)`, replace the `if` expression with the contents of the `else` expression.
Changes:
- Add `isMangledIdent` to determine if `fmtIdent` would make any edits to the identifier
- Any function that has a mangled identifier is referred to using the mangled identifer
within the current file, but if it is exported the first export will be with the non-mangled name.
- Add `zig_import` to import a symbol under a different name
- Add a level of indirection to float function names. Now, they are referred to as
`zig_float_fn_<float type>_<operation>`. The definitions in zig.h are wrapped
with `zig_import` to import the symbol under the real name.
The specific problem that sparked this change was the combination of
`zig_libc_name_f80(name) __##name##x` with the input `fma`, resulting
in `__fmax`, which is a new intrinsic in recent versions of cl.exe.
With the above changes in place, compiler_rt can output the following:
```
static zig_weak_linkage_fn zig_f80 zig_e___fmax(zig_f80, zig_f80, zig_f80);
zig_export(zig_weak_linkage_fn zig_f80 zig_e___fmax(zig_f80, zig_f80, zig_f80), __fmax, "__fmax");
```
Within compiler_rt, `zig_e___fmax` is used to refer to the function, but consumers
will import `__fmax`, which maps to their `zig_float_fn_f80_fma` definition from zig.h.
* don't reset the rng. it seems like it was getting stuck trying the
same transforms over and over again.
* slide the window over after failing a large transform set, idea being
that transformations in the failed set are more likely to be
problematic.
and use that to fix up usused variable declarations and parameters that
are caused by transformations.
also add a transformation to replace global variable init with
`undefined`.
