urelibs: break cyclic dependency; treat regcompare as build tool

Build tools do not link against merged libraries but individual small
ones we need for this (gb_BUILD_HELPER_LIBS).

Change-Id: Ia765e11a93ed05d126334a3e146fb88e368954ac

solenv/gbuild/LinkTarget.mk

@@ -873,6 +873,7 @@ gb_BUILD_HELPER_LIBS := basegfx \
 gb_BUILD_HELPER_TOOLS := cppumaker \
 	idlc \
 	reg2unoidl \
+	regcompare \
 	regmerge \
 	rsc \
 	svidl