When source directory can be arrived at by two paths,
configure might misdetect an out of tree build.
The simplest way to trigger the problem is running
configure using a full path. E.g. (<firstpath> refers to qemu source
tree):
    ln -s <firstpath> <secondpath>
    cd <firstpath>
    <secondpath>/configure

A more practical way is when make runs configure automatically:

1. cd <firstpath>/; ./configure
    SRC_PATH=<firstpath>/ is written into config_host.mak
2. cd <secondpath>/; touch configure; make
    make now runs <firstpath>/configure, so configure
    assumes it's an out of tree build

When this happens configure overwrites parts of
the current tree with symlinks.

Make the test more robust: look for configure
in the current directory.
If there - we know it's a source build!
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>