This fixes build with dev-build/slibtool

--- gtk-engines-2.20.2/configure.ac
+++ gtk-engines-2.20.2/configure.ac
@@ -27,6 +27,9 @@
 AC_DEFINE_UNQUOTED([GETTEXT_PACKAGE],["$GETTEXT_PACKAGE"],[Gettext package])
 AM_GLIB_GNU_GETTEXT
 
+AC_CHECK_LIBM
+AC_SUBST([LIBM])
+
 AC_ARG_ENABLE(all, 		[  --disable-all           skip all engines/themes by default], [defaultval=$enableval], 	[defaultval="yes"])
 AC_ARG_ENABLE(clearlooks, 	[  --disable-clearlooks    skip ClearLooks engine/theme], 	[clearlooks=$enableval], 	[clearlooks="$defaultval"])
 AC_ARG_ENABLE(crux, 		[  --disable-crux          skip Crux engine/theme], 		[crux=$enableval], 		[crux="$defaultval"])
--- gtk-engines-2.20.2/engines/hc/Makefile.am
+++ gtk-engines-2.20.2/engines/hc/Makefile.am
@@ -38,7 +38,7 @@
 	./src/hc-style.c
 
 libhcengine_la_LDFLAGS = -module -avoid-version -no-undefined -export-symbols $(top_srcdir)/engines/engine.symbols
-libhcengine_la_LIBADD = $(top_builddir)/engines/support/libsupport.la $(GTK_LIBS)
+libhcengine_la_LIBADD = $(top_builddir)/engines/support/libsupport.la $(GTK_LIBS) $(LIBM)
 
 -include $(top_srcdir)/git.mk
 
--- gtk-engines-2.20.2/engines/mist/Makefile.am
+++ gtk-engines-2.20.2/engines/mist/Makefile.am
@@ -16,7 +16,7 @@
 	./src/mist.c
 
 libmist_la_LDFLAGS = -module -avoid-version -no-undefined -export-symbols $(top_srcdir)/engines/engine.symbols
-libmist_la_LIBADD = $(top_builddir)/engines/support/libsupport.la $(GTK_LIBS)
+libmist_la_LIBADD = $(top_builddir)/engines/support/libsupport.la $(GTK_LIBS) $(LIBM)
 
 -include $(top_srcdir)/git.mk
 
--- gtk-engines-2.20.2/engines/thinice/Makefile.am
+++ gtk-engines-2.20.2/engines/thinice/Makefile.am
@@ -18,7 +18,7 @@
 	./src/thinice_main.c
 
 libthinice_la_LDFLAGS = -module -avoid-version -no-undefined -export-symbols $(top_srcdir)/engines/engine.symbols
-libthinice_la_LIBADD = $(top_builddir)/engines/support/libsupport.la $(GTK_LIBS)
+libthinice_la_LIBADD = $(top_builddir)/engines/support/libsupport.la $(GTK_LIBS) $(LIBM)
 
 -include $(top_srcdir)/git.mk