Update warnings with info from Krister

See also: https://kristerw.blogspot.se/2017/09/useful-gcc-warning-options-not-enabled.html

Author: lefticus

02-Use_the_Tools_Available.md

@@ -94,11 +94,18 @@ You should use as many compilers as you can for your platform(s). Each compiler
  * `-Wcast-align` warn for potential performance problem casts
  * `-Wunused` warn on anything being unused
  * `-Woverloaded-virtual` warn if you overload (not override) a virtual function
- * `-pedantic`
+ * `-Wpedantic` warn if non-standard C++ is used
  * `-Wconversion` warn on type conversions that may lose data
  * `-Wsign-conversion` warn on sign conversions
  * `-Wmisleading-indentation` warn if identation implies blocks where blocks do not exist
-
+ * `-Wduplicated-cond` warn if `if` / `else` chain has duplicated conditions
+ * `-Wduplicated-branches` warn if `if` / `else` branches have duplicated code
+ * `-Wlogical-op` warn about logical operations being used where bitwise were probably wanted
+ * `-Wnull-dereference` warn if a null dereference is detected
+ * `-Wuseless-cast` warn if you perform a cast to the same type
+ * `-Wdouble-promotion` warn if `float` is implicit promoted to `double`
+ * `-Wformat=2` warn on security issues around functions that format output (ie `printf`)
+ 
 Consider using `-Weverything` and disabling the few warnings you need to on Clang