@Kha
I was having several errors of the form
```
224: /Users/leonardodemoura/projects/lean4/build/release/stage0.5/bin/../include/lean/runtime/exception.h:23:13: error: exception specification of overriding function is more lax than base version
224: virtual ~throwable() noexcept;
224: ^
224: /Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../include/c++/v1/exception:102:13: note: overridden virtual function is here
224: virtual ~exception() _NOEXCEPT;
224: ^
224: In file included from myfuns.cpp:1:
```
As far as I can tell, the error ocurrs because my compiler uses an old
C++ standard if the option `-std` is not used.
I guess `-std=c++11` would also works, but I decided to use the same
standard we used to compile Lean.
Since we don't use static initializers, really the only difference between using `clang` and `clang++` is the default
inclusion of the C++ standard library.
@dselsam @kha
I did not have to create a new shared library.
The main limitation of this approach is that the new `extern`
functions are only available in compile code. That is, we cannot use
them with `#eval`.
We cannot implement `DecidableEq Float` using C equality for
`double`. Reason: the C implementation is not even reflexive.
If we need `DecidableEq Float`, we will need to provide our own
implementation (i.e., a wrapper around the one provided by the
hardware). In this commit, we implement `HasBeq Float` instead.
cc @dselsam
Preparation for new unifier.
@dselsam: I had to make minor changes at `Synth.Lean`, and add messy
code to `Context.lean`. `Context.lean` will be deleted in the future.
So, it is not a big deal.
