I am building gimp via pkgsrc on NetBSD 4.0ish (i386), and have enabled the use of parallel builds via MAKE_JOBS=3, which passes -j3 to gmake to build gimp.  This mostly works, but I have encountered several failures in libgimpthumb.   The problem seems to be that the LDADD value for gimp-thumbnail-list ends up being ../libgimpthumb/libgimpthumb-2-0.la, and this somehow isn't matched up with the dependencies to make the library.  So, make chokes on gimp-thumbnail-list.  Rerunning it seems to help, as it's then there.  I am not really clear on make's rules, but I suggest not using a relative path for the LDADD value would help.  I  removed the ../libgimpthumb/ before the .la in Makefile and the build ran the first time.

Also, gimp-thumbnail-list-SURCES is a typo, but I think the default value is working.

Here's my make output from the failing build:

Making all in libgimpthumb
gmake[2]: Entering directory `/n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/gimp-2.3.18/libgimpthumb'
/bin/sh ../libtool --tag=CC --mode=link cc  -O2 -I/usr/pkg/include -I/usr/include -I/usr/pkg/include/freetype2 -I/usr/X11R6/include -Wall -Wdeclaration-after-statem
ent -Wmissing-prototypes -Wmissing-declarations -Winit-self -Wpointer-arith  -Wl,-E -L/usr/pkg/lib -Wl,-R/usr/pkg/lib -L/usr/lib -Wl,-R/usr/lib -L/usr/X11R6/lib -Wl
,-R/usr/X11R6/lib -o libgimpthumb-2.0.la -rpath /usr/pkg/lib -version-info 318:0:318   gimpthumb-enums.lo gimpthumb-error.lo gimpthumb-utils.lo gimpthumbnail.lo ../
libgimpmath/libgimpmath-2.0.la -Wl,-R/usr/pkg/lib -L/usr/pkg/lib -lgdk_pixbuf-2.0 -lm -lgobject-2.0 -lgmodule-2.0 -lglib-2.0 -lintl   
gmake[2]: *** No rule to make target `../libgimpthumb/libgimpthumb-2.0.la', needed by `gimp-thumbnail-list'.  Stop.
gmake[2]: *** Waiting for unfinished jobs....
cc -shared  .libs/gimpthumb-enums.o .libs/gimpthumb-error.o .libs/gimpthumb-utils.o .libs/gimpthumbnail.o  -Wl,--rpath -Wl,/n0/gdt/NetBSD-current/pkgsrc/graphics/gi
mp24/work/gimp-2.3.18/libgimpmath/.libs -Wl,--rpath -Wl,/n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib -Wl,--rpath -Wl,/usr/pkg/lib -Wl,--rpath -
Wl,/n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib -L/n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib -L/n0/gdt/NetBSD-current/pk
gsrc/graphics/gimp24/work/.x11-buildlink/lib ../libgimpmath/.libs/libgimpmath-2.0.so /n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib/libgdk_pixbuf
-2.0.so -lm /n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib/libgobject-2.0.so /n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib/li
bgmodule-2.0.so /n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/.buildlink/lib/libglib-2.0.so -lintl  -Wl,-E -Wl,-R/usr/pkg/lib -Wl,-R/usr/X11R6/lib -Wl,-soname 
-Wl,libgimpthumb-2.0.so.0 -o .libs/libgimpthumb-2.0.so.0.318.0
(cd .libs && rm -f libgimpthumb-2.0.so.0 && ln -s libgimpthumb-2.0.so.0.318.0 libgimpthumb-2.0.so.0)
(cd .libs && rm -f libgimpthumb-2.0.so && ln -s libgimpthumb-2.0.so.0.318.0 libgimpthumb-2.0.so)
ar cru .libs/libgimpthumb-2.0.a  gimpthumb-enums.o gimpthumb-error.o gimpthumb-utils.o gimpthumbnail.o
ranlib .libs/libgimpthumb-2.0.a
creating libgimpthumb-2.0.la
(cd .libs && rm -f libgimpthumb-2.0.la && ln -s ../libgimpthumb-2.0.la libgimpthumb-2.0.la)
gmake[2]: Leaving directory `/n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/gimp-2.3.18/libgimpthumb'
gmake[1]: *** [all-recursive] Error 1
gmake[1]: Leaving directory `/n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24/work/gimp-2.3.18'
gmake: *** [all] Error 2
*** Error code 2

Stop.
make: stopped in /n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24
*** Error code 1

Stop.
make: stopped in /n0/gdt/NetBSD-current/pkgsrc/graphics/gimp24