Revert "vmtests: revert to Clang/LLVM 12 until Clang 13 regression is fixed"

Clang 13 now has the fix for the original regression, time to get back to
using nightly versions.

This reverts commit adaf538bca.

travis-ci/vmtest/build_selftests.sh

@@ -8,7 +8,7 @@ travis_fold start prepare_selftests "Building selftests"
 
 sudo apt-get -y install python-docutils # for rst2man
 
-LLVM_VER=12
+LLVM_VER=13
 LIBBPF_PATH="${REPO_ROOT}"
 REPO_PATH="travis-ci/vmtest/bpf-next"
 

travis-ci/vmtest/run_vmtest.sh

@@ -15,9 +15,9 @@ ${VMTEST_ROOT}/build_pahole.sh travis-ci/vmtest/pahole
 travis_fold start install_clang "Installing Clang/LLVM"
 
 wget -O - https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
-sudo add-apt-repository "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-12 main"
+sudo add-apt-repository "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic main"
 sudo apt-get update
-sudo apt-get install -y clang-12 lld-12 llvm-12
+sudo apt-get install -y clang-13 lld-13 llvm-13
 
 travis_fold end install_clang