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 both VPATH builds and the gnulib symfiles machinery.

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 6a6059f779c9ebb39f6011c2285afa93365139ea..6bba07ea3a95f69fcb47457dde0970a72eecbcee 160000 (submodule)
--- a/common
+++ b/common
@@ -1 +1 @@
-Subproject commit 6a6059f779c9ebb39f6011c2285afa93365139ea
+Subproject commit 6bba07ea3a95f69fcb47457dde0970a72eecbcee