Check if json.gz files exist, not the gcov version.

Different versions of gcov output different types of files; older
versions output textual data, newer ones output compressed JSON files
(the switch happens in gcov).

"llvm-cov gcov" is supposed to be compatible with gcov, but never
outputs compressed JSON files. This means the version check will break
if gcov is substituted with this tool.

Checking for the output files created should avoid this issue, and be a
more robust check overall.

Fixes #18874

tools/test/collect_cc_coverage.sh

@@ -150,15 +150,10 @@ function gcov_coverage() {
           # https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84879).
           "${GCOV}" -i $COVERAGE_GCOV_OPTIONS -o "$(dirname ${gcda})" "${gcda}"
 
-          # Extract gcov's version: the output of `gcov --version` contains the
-          # version as a set of major-minor-patch numbers, of which we extract
-          # the major version.
-          gcov_major_version=$("${GCOV}" --version | sed -n -E -e 's/^.*\s([0-9]+)\.[0-9]+\.[0-9]+\s?.*$/\1/p')
-
-          # Check the gcov version so we can process the data correctly
-          if [[ $gcov_major_version -ge 9 ]]; then
-              # gcov 9 or higher use a JSON based format for their coverage reports.
-              # The output is generated into multiple files: "$(basename ${gcda}).gcov.json.gz"
+          # Check the type of output: gcov 9 or later outputs compressed JSON
+          # files, but earlier versions of gcov, and all versions of llvm-cov,
+          # do not. These output textual information.
+          if stat --printf='' *.gcov.json.gz > /dev/null 2>&1; then
               # Concatenating JSON documents does not yield a valid document, so they are moved individually
               mv -- *.gcov.json.gz "$(dirname "$output_file")/$(dirname ${gcno_path})"
           else