+- Fix false positives from cmake which probes for compiler flags without
+ setting CPPFLAGS; reported and suggested fix by Joao Eriberto Mota Filho
+ (Debian Bug #994422).
+- Properly handle quoted flags; reported by Olek Wojnar (see Debian Bug
+ #975650 message 45).
+- Strip (basic) environment variables before compiler detection to reduce
+ false positives; reported by Fabian Wolff (Debian Bug #975650)