Compile errors with ldc-build-runtime --testrunners

[Jacob Carlborg]

I’m running the ldc-build-runtime tool to build druntime and phobos. 
This compiles fine, but when I add the `--testrunners` flag I get a 
compile error in phobos:

std/bigint.d(855): Error: cannot take address of local `resultBits` in 
`@safe` function `toFloatTruncating`
std/bigint.d(954): Error: template instance 
`std.bigint.BigInt.toFloatTruncating!float` error instantiating
std/bigint.d(667):        instantiated from here: `opCmp!float`
std/bigint.d(676):        instantiated from here: `opEquals!float`

I don’t see how that would ever compile. Why hasn’t that been caught by 
the CI pipelines?

https://github.com/ldc-developers/phobos/blob/26d14c1a292267a32ce64fa7f219acc3d3cca274/std/bigint.d#L855 


-- 
/Jacob Carlborg