Please relace the vtree.h #pragma change of this commit with a better
solution once you have one.

777e03ba had the disadvantage that it
requires all vmods to adjust their build, besides affecting more code
than necessary.

Under the assumption that the issue with VRBT is not acutally a
violation of strict aliasing, but rather only a violation of gcc's
pedantic "compatible lvalue rule", we silence gcc warnings rather than
turning off strict aliasing.

Note that this is more convenient, but also more dangerous, because we
fail to catch any actual strict aliasing errors where vtree.h is used.

This reverts commit 777e03ba.