Ninja generator doesn't need Windows backslash
It seems that Ninja generator may not need to have backslashes
\ hardcoded on Windows. Per Brad King's suggestion, I removed the hard-coding and tested with Ninja 1.10.0 on Windows 10 and:
- MinGW 10.2
- Visual Studio 2019
I observed that with MinGW, the build.ninja has all
/, while Visual Studio still has
\. Since the compiler used in #21022 is a GCC cross-compiler, it seems likely this fixes that issue while not seeming to break other things.