Github: Enforce expected amount of cxa_atexit registrations

There is only one registration that I've not been able to track down why
it happens, but it is something to do with std::ostream. This just
ensures in CI that we don't ever register anymore atexit handlers so we
don't regress on crashing on `exit`.

Author: Sonicadvance1

.github/workflows/ccpp.yml

@@ -233,6 +233,11 @@ jobs:
       working-directory: ${{runner.workspace}}/build
       run: mv ${{runner.workspace}}/build/Testing/Temporary/LastTest.log ${{runner.workspace}}/build/Testing/Temporary/LastTest_StructVerifier.log || true
 
+    - name: Ensure expected atexit registrations
+      working-directory: ${{runner.workspace}}/build
+      shell: bash
+      run: $GITHUB_WORKSPACE/Scripts/CountInstancesOfAtExit.py ${{runner.workspace}}/build/Bin/FEX "__cxa_atexit@plt>$" 1 ; echo $?
+
     - name: Truncate test results
       if: ${{ always() }}
       shell: bash

Scripts/CountInstancesOfAtExit.py

@@ -0,0 +1,21 @@
+#!/usr/bin/python3
+import sys
+import subprocess
+
+def main():
+    # Args: <FEX bin> <string> <count>
+    if (len(sys.argv) < 4):
+        sys.exit()
+
+    result = subprocess.run(['sh', '-c', "llvm-objdump -D {} | grep \'{}\' | wc -l".format(sys.argv[1], sys.argv[2])], stdout=subprocess.PIPE)
+    Count = int(result.stdout.decode('ascii'))
+
+    if (Count != int(sys.argv[3])):
+        sys.exit(-1)
+
+    return 0
+
+if __name__ == "__main__":
+    # execute only if run as a script
+    sys.exit(main())
+