meson: fix relpath failure on Win32

On win32, os.path.relpath can raise an exception when computing
for example C:/msys64/mingw64/x.exe relative to E:/path/qemu-build.
Use try...except to avoid this, just using an absolute path in
this case.

Signed-off-by: Yonggang Luo <luoyonggang@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

scripts/mtest2make.py

@@ -53,9 +53,16 @@ def __init__(self):
 for test in json.load(sys.stdin):
     env = ' '.join(('%s=%s' % (shlex.quote(k), shlex.quote(v))
                     for k, v in test['env'].items()))
-    executable = os.path.relpath(test['cmd'][0])
+    executable = test['cmd'][0]
+    try:
+        executable = os.path.relpath(executable)
+    except:
+        pass
     if test['workdir'] is not None:
-        test['cmd'][0] = os.path.relpath(test['cmd'][0], test['workdir'])
+        try:
+            test['cmd'][0] = os.path.relpath(executable, test['workdir'])
+        except:
+            test['cmd'][0] = executable
     else:
         test['cmd'][0] = executable
     cmd = '$(.test.env) %s %s' % (env, ' '.join((shlex.quote(x) for x in test['cmd'])))