try_compile does not respect TARGET_CFLAGS

[jschwe]

While trying to cross-compile servo on a windows host, I noticed that the mozjs try_compile configure checks don't pass any flags from TARGET_CFLAGS or TARGET_CXXFLAGS, which in my case contain the sysroot. With the sysroot flag missing one of the try_compile checks fails, since it can't find a header file (features.h). I'm not sure why I don't experience this on my Linux machine - perhaps the compiler falls back to the host sysroot (which would also be wrong).

[jschwe]

Closing this issue. It seems that replacing backslashes with forward slashes (see #478) also causes all try_compile invocations to succeed again.