Cross compiling tools / qemu-img results in "ninja: no work to do"
Description of problem:
I have the following Dockerfile setting up a cross-compile environment for QEMU.
I am trying to build qemu-img.exe only at the moment


```
FROM fedora as builder
RUN --mount=type=cache,target=/var/cache \
        dnf -v install --assumeyes strace gcc make mingw64-gcc mingw64-binutils python-setuptools meson mingw64-glib2-static mingw64-glib2 diffutils

FROM builder as qemu-builder
WORKDIR /src/qemu #assuming qemu source tree is already available at /src/qemu
RUN
RUN ./configure --cross-prefix=x86_64-w64-mingw32- --target-list='' --static
RUN make V=1 tools
```
With either `make tools` or `make qemu-img.exe` I get

```
#10 0.265 changing dir to build for make "tools"...
#10 0.267 make[1]: Entering directory '/src/qemu/build'
#10 0.330 ninja: no work to do.
#10 0.331 { \
#10 0.331   echo 'ninja-targets = \'; \
#10 0.331   /usr/bin/ninja -t targets all | sed 's/:.*//; $!s/$/ \\/'; \
#10 0.331   echo 'build-files = \'; \
#10 0.331   /usr/bin/ninja -t query build.ninja | sed -n '1,/^  input:/d; /^  outputs:/q; s/$/ \\/p'; \
#10 0.331 } > Makefile.ninja.tmp && mv Makefile.ninja.tmp Makefile.ninja
#10 0.363 /src/qemu/build/pyvenv/bin/meson introspect --targets --tests --benchmarks | /src/qemu/build/pyvenv/bin/python3 -B scripts/mtest2make.py > Makefile.mtest
#10 0.634 make[1]: Nothing to be done for 'tools'.
#10 0.634 make[1]: Leaving directory '/src/qemu/build'
#10 DONE 0.6s
```

Following the info in `make help`, I tried `make qemu-img.o` which resulted in

```
cc    -c -o qemu-img.o qemu-img.c
qemu-img.c:25:10: fatal error: qemu/osdep.h: No such file or directory
   25 | #include "qemu/osdep.h"
      |          ^~~~~~~~~~~~~~
```
Additional information: