Get back to 100% coverage

Closes #30

This is achieved by running libfuzzer with USE_32_BIT_VERSIONS={OFF,ON},
and then combining the corpora. I suspect that the problem earlier was
that we only had the 32 bit corpus but were measuring coverage for 64
bit in jenkins.

Jenkinsfile

@@ -123,8 +123,7 @@ pipeline {
                 '''
                 recordCoverage qualityGates: [[criticality: 'NOTE', metric: 'MODULE']], tools: [[parser: 'COBERTURA', pattern: 'build/coverage.xml']]
                 sh '''
-                # Temporarily remove until we finish the transition to 32-bit versions
-                # gcovr -f ConflictSet.cpp --fail-under-line 100 > /dev/null
+                gcovr -f ConflictSet.cpp --fail-under-line 100 > /dev/null
                 '''
             }
         }