ci: Use clang-snapshot in "MSan" job

Author: hebasto

.github/workflows/ci.yml

@@ -440,7 +440,7 @@ jobs:
       SCHNORRSIG: 'yes'
       MUSIG: 'yes'
       ELLSWIFT: 'yes'
-      CC: 'clang'
+      CC: 'clang-snapshot'
       SECP256K1_TEST_ITERS: 32
       ASM: 'no'
       WITH_VALGRIND: 'no'

ci/linux-debian.Dockerfile

@@ -70,7 +70,7 @@ RUN \
     # Determine the version number of the LLVM development branch
     LLVM_VERSION=$(apt-cache search --names-only '^clang-[0-9]+$' | sort -V | tail -1 | cut -f1 -d" " | cut -f2 -d"-" ) && \
     # Install
-    apt-get install --no-install-recommends -y "clang-${LLVM_VERSION}" && \
+    apt-get install --no-install-recommends -y "clang-${LLVM_VERSION}" "libclang-rt-${LLVM_VERSION}-dev" && \
     # Create symlink
     ln -s "/usr/bin/clang-${LLVM_VERSION}" /usr/bin/clang-snapshot && \
     # Clean up