Windows builds use external assembler

[vadimcn]

Windows builds currently use external assembler for the sake of generating correct stack unwinding tables (see #8596). This, of course, slows down the build and also creates a dependency on the assembler tool.

Eventually it would be nice to figure out what's wrong with LLVM's integrated assembler, and switch back to using it.

[ILyoan]

Now we have upgraded llvm which contains patches for arm unwind table generation.
Thus I think we can turn off the android-ndk assembly pass. I'll take look at it.

[sanxiyn]

Android half is fixed in #8931.