bumpmap: uses sqrt(3).
colomod: uses pow(3).

--- src/modules/filters/Makefile.in.orig	2008-10-21 05:02:00.000000000 +0200
+++ src/modules/filters/Makefile.in	2012-01-14 16:24:41.858233130 +0100
@@ -225,10 +225,10 @@ testfilter_la_LDFLAGS = -module -avoid-v
 testfilter_la_LIBADD = $(top_builddir)/src/lib/libImlib2.la
 bumpmap_la_SOURCES = filter_bumpmap.c
 bumpmap_la_LDFLAGS = -module -avoid-version
-bumpmap_la_LIBADD = $(top_builddir)/src/lib/libImlib2.la
+bumpmap_la_LIBADD = $(top_builddir)/src/lib/libImlib2.la -lm
 colormod_la_SOURCES = filter_colormod.c
 colormod_la_LDFLAGS = -module -avoid-version
-colormod_la_LIBADD = $(top_builddir)/src/lib/libImlib2.la
+colormod_la_LIBADD = $(top_builddir)/src/lib/libImlib2.la -lm
 all: all-am
 
 .SUFFIXES: