It will be the system library installed in /usr/ that is still being used

--prefix=/usr

will overwrite the system libgphoto2 library.

Unfortunately, now when I run sudo make, I get stuck in a loop:
mv -f $depbase.Tpo $depbase.Plo
libtool: compile: gcc -DHAVE_CONFIG_H -I. -I.. -D_GPHOTO2_INTERNAL_CODE -DLOCALEDIR="/usr/share/locale" -DCAMLIBS="/usr/lib/libgphoto2/2.5.10" -I.. -I.. -I../libgphoto2_port -I../libgphoto2 -I../libgphoto2 -g -O2 -Wall -Wmissing-declarations -Wmissing-prototypes -MT soundvision/soundvision.lo -MD -MP -MF soundvision/.deps/soundvision.Tpo -c soundvision/soundvision.c -fPIC -DPIC -o soundvision/.libs/soundvision.o
depbase=echo soundvision/agfa_cl18.lo | sed 's|[^/]*$|.deps/&|;s|\.lo$||';
/bin/bash ../libtool --tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I. -I.. -D_GPHOTO2_INTERNAL_CODE -DLOCALEDIR="/usr/share/locale" -DCAMLIBS="/usr/lib/libgphoto2/2.5.10" -I.. -I.. -I../libgphoto2_port -I../libgphoto2 -I../libgphoto2 -g -O2 -Wall -Wmissing-declarations -Wmissing-prototypes -MT soundvision/agfa_cl18.lo -MD -MP -MF $depbase.Tpo -c -o soundvision/agfa_cl18.lo soundvision/agfa_cl18.c &&
mv -f $depbase.Tpo $depbase.Plo

It then repeats over and over. As well, it does the same thing for sudo make check.

if there is a loop, there likely is inconsistent time on the device, the device running in the future or past.