libethumb: add patch to fix static builds

libethumb: add patch to fix static builds

Fixes:
http://autobuild.buildroot.net/results/060/060c4b7303976994a13ecd286e936fee59c7a095/
http://autobuild.buildroot.net/results/d01/d0111a8524f74c6bc596d85289addbed0e77f8c6/
http://autobuild.buildroot.net/results/147/1471f8a4838369ed825da406f88aae425465e827/
http://autobuild.buildroot.net/results/a35/a35a39fee7c24abe0bbe12d71bebf92005367391/

And many more.

Ethumb includes dlfcn.h even though it isn't used, breaking builds with
purely static toolchains.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>