Azure/GitLab: Switch over to using LLVM-10

At this point LLVM-7 is rather old.  Switch over to LLVM-10 to enable
some amount of CI coverage with newer compilers.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/.azure-pipelines.yml b/.azure-pipelines.yml
index a043d29..5d96454 100644
--- a/.azure-pipelines.yml
+++ b/.azure-pipelines.yml
@@ -161,7 +161,7 @@
           TEST_PY_BD: "sandbox"
         sandbox_clang:
           TEST_PY_BD: "sandbox"
-          OVERRIDE: "-O clang-7"
+          OVERRIDE: "-O clang-10"
         sandbox_spl:
           TEST_PY_BD: "sandbox_spl"
           TEST_PY_TEST_SPEC: "test_ofplatdata or test_handoff"