buildroot

libcgi: add patch to fix static library building

The new libcgi build system was forcing the build of a shared library,
breaking the build on static-only configurations. This commit adds a
libcgi patch (submitted upstream) that makes its build system use the
default CMake behavior (rely on BUILD_SHARED_LIBS).

Fixes:

  http://autobuild.buildroot.net/results/c166aa1eda9d86083a1aeefd8631ed45dbcb05e7/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>