The latest liboil (0.3.7) fails to rebuild for me on PPC, whereas 0.3.6 did
fine. You can find the build log here :

http://buildsys.fedoraproject.org/logs/fedora-development-extras/5931-liboil-0.3.7-3.fc5/ppc/build.log

The relevant bit is :
[...]
 gcc -DHAVE_CONFIG_H -I. -I. -I../.. -Wall -Wa,-mregnames -D_BSD_SOURCE
-D_GNU_SOURCE -I../.. -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
-fstack-protector --param=ssp-buffer-size=4 -m32 -MT libpowerpc_la-clip.lo -MD
-MP -MF .deps/libpowerpc_la-clip.Tpo -c clip.c -o libpowerpc_la-clip.o
>/dev/null 2>&1
if /bin/sh ../../libtool --tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I. -I.
-I../..    -Wall -Wa,-mregnames -D_BSD_SOURCE -D_GNU_SOURCE -I../.. -O2 -g -pipe
-Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector
--param=ssp-buffer-size=4 -m32 -MT libpowerpc_la-conv.lo -MD -MP -MF
".deps/libpowerpc_la-conv.Tpo" -c -o libpowerpc_la-conv.lo `test -f 'conv.c' ||
echo './'`conv.c; \
then mv -f ".deps/libpowerpc_la-conv.Tpo" ".deps/libpowerpc_la-conv.Plo"; else
rm -f ".deps/libpowerpc_la-conv.Tpo"; exit 1; fi
 gcc -DHAVE_CONFIG_H -I. -I. -I../.. -Wall -Wa,-mregnames -D_BSD_SOURCE
-D_GNU_SOURCE -I../.. -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions
-fstack-protector --param=ssp-buffer-size=4 -m32 -MT libpowerpc_la-conv.lo -MD
-MP -MF .deps/libpowerpc_la-conv.Tpo -c conv.c  -fPIC -DPIC -o
.libs/libpowerpc_la-conv.o
conv.c:78: error: expected ')' before '*' token
conv.c:78: error: 'clipconv_s8_f32_powerpc' undeclared here (not in a function)
conv.c:79: error: expected ')' before '*' token
conv.c:79: error: 'clipconv_u8_f32_powerpc' undeclared here (not in a function)
conv.c:80: error: expected ')' before '*' token
conv.c:80: error: 'clipconv_s16_f32_powerpc' undeclared here (not in a function)
conv.c:81: error: expected ')' before '*' token
[... etc ...]