qemu: rename VERSION to QEMU_VERSION to avoid name clash

In libc++ starting with LLVM8 there's `<version>` include in `cstddef`:

The following things also align:

* QEMU has a file called `VERSION` in repo root
* QEMU prepends repo root to include path in build
* macOS has a case-insensetive filesystem

All of this combined means that `VERSION` file is included as a header.

Working around this be renaming `VERSION` -> `QEMU_VERSION` to resolve ambiguity.

The problem really only appears on `aarch64-darwin`, since on `x86_64-darwin`
there are no C++ files to compile. The workaround is harmless enough to apply.

pkgs/applications/virtualization/qemu/default.nix

@@ -108,6 +108,10 @@ stdenv.mkDerivation rec {
     # this script isn't marked as executable b/c it's indirectly used by meson. Needed to patch its shebang
     chmod +x ./scripts/shaderinclude.pl
     patchShebangs .
+    # avoid conflicts with libc++ include for <version>
+    mv VERSION QEMU_VERSION
+    substituteInPlace meson.build \
+      --replace "'VERSION'" "'QEMU_VERSION'"
   '' + optionalString stdenv.hostPlatform.isMusl ''
     NIX_CFLAGS_COMPILE+=" -D_LINUX_SYSINFO_H"
   '';