Dockerfile: adding required libraries for checkers
Dockerfile: adding required libraries for checkers

clang needs 2 more files, `ld` which is provided by binutils and
`crtbegin.o` which is provided by libgcc-5-dev.

Signed-off-by: André Martins <bc9800b9d52a24cce72a73dd528afed53f10e5fc@cilium.io>

cilium-team/cilium,cilium/cilium,scanf/cilium,gumpt/cilium,gumpt/cilium,michi-covalent/cilium,eloycoto/cilium,tgraf/cilium,eloycoto/cilium,eloycoto/cilium,tgraf/cilium,tgraf/cilium,gumpt/cilium,cilium/cilium,scanf/cilium,scanf/cilium,scanf/cilium,eloycoto/cilium,gumpt/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,cilium/cilium,mskarbek/cilium,eloycoto/cilium,scanf/cilium,mskarbek/cilium,tklauser/cilium,tklauser/cilium,mskarbek/cilium,mskarbek/cilium,eloycoto/cilium,tklauser/cilium,gumpt/cilium,michi-covalent/cilium,eloycoto/cilium,gumpt/cilium,cilium/cilium,michi-covalent/cilium,scanf/cilium,gumpt/cilium,mskarbek/cilium,cilium-team/cilium,mskarbek/cilium,tklauser/cilium,tklauser/cilium,scanf/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium