pkg/csource: exclude linux/arm64 tests
pkg/csource: exclude linux/arm64 tests

I think I misinterpreted the error that episodically happens on ci:

collect2: error: ld terminated with signal 11 [Segmentation fault], core dumped
compiler invocation: aarch64-linux-gnu-gcc [-Wall -Werror -O1 -g -o /tmp/syz-executor570589071 -pthread -DGOOS_linux=1 -DGOARCH_arm64=1 -x c - -static]

as OOM, but they all involve aarch64-linux-gnu-gcc:

https://travis-ci.org/google/syzkaller/jobs/461827347
https://travis-ci.org/google/syzkaller/jobs/460226110
https://travis-ci.org/google/syzkaller/jobs/463564291

So I guess the problem can be with the arm64 toolchain that just crashes randomly.

xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,google/syzkaller,xairy/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller,xairy/syzkaller,google/syzkaller