check_software: tolerate libquadmath in ldd check

that is part of gcc-10 and the system libquatmath can be linked if built with system gcc-10.

slapos/testing/check_software.py

@@ -77,6 +77,7 @@ def checkSoftware(slap, software_url):
       'libresolv',
       'librt',
       'libstdc++',
+      'libquadmath',
       'libutil',
   ))