Bump dxcommon to fix builds using --disable-dependency-tracking.

Some build rules were inadvertently depending on directory creation that
happens as a side effect of depfiles generation.  This does not happen
when configuring with --disable-dependency-tracking, leading to issues
with VPATH builds.

Failures are easily observed with a command like

  make DISTCHECK_CONFIGURE_FLAGS=--disable-dependency-tracking distcheck

Using parallel make can hide problems since it seems Automake also
generates make rules that incidentally create these directories.

diff --git a/common b/common
index 6532aaac91a7efd99eb74726679c4000459e7bb3..6bba07ea3a95f69fcb47457dde0970a72eecbcee 160000 (submodule)
--- a/common
+++ b/common
@@ -1 +1 @@
-Subproject commit 6532aaac91a7efd99eb74726679c4000459e7bb3
+Subproject commit 6bba07ea3a95f69fcb47457dde0970a72eecbcee