Prefer plain scan-build-py command if available

Debian added the symlink with llvm-defaults 0.61 [1], in Sid as of
this writing.

[1] https://tracker.debian.org/news/1576545/accepted-llvm-defaults-061-source-into-unstable/

support/scan-build-wrapper.sh

@@ -1,8 +1,17 @@
 #!/bin/sh
 
-# find the current default LLVM version and its scan-build-py
-llvm_version="$(readlink $(command -v scan-build) | cut -d '-' -f 3)"
-SCAN_BUILD_PY="$(command -v scan-build-py-${llvm_version})"
+bin="scan-build-py"
+SCAN_BUILD_PY="$(command -v ${bin})"
+if [ -z "${SCAN_BUILD_PY}" ]; then
+    # find the current default LLVM version and its scan-build-py
+    llvm_version="$(readlink $(command -v scan-build) | cut -d '-' -f 3)"
+    SCAN_BUILD_PY="$(command -v ${bin}-${llvm_version})"
+fi
+
+if [ -z "${SCAN_BUILD_PY}" ]; then
+    echo "ERROR: ${bin} not found!" >&2
+    exit 1
+fi
 
 # run it to produce SARIF and HTML output with Clang
 exec "${SCAN_BUILD_PY}" --sarif-html --use-cc=clang "$@"