Backport compiler flags for gcc-12

CMake/Settings.cmake

@@ -17,6 +17,13 @@ set(COMPILER_FLAGS
   -pedantic
   -Wpedantic
   -Wunused
+   # FIXME: The following bunch are needed for gcc12 atm.
+   -Wno-missing-requires
+   -Wno-restrict
+   -Wno-null-dereference
+   -Wno-maybe-uninitialized
+   -Wno-unknown-warning-option # and this to work with clang
+   # TODO: Address these and others in https://github.com/XRPLF/clio/issues/1273
 )
 
 #TODO: reenable when we change CI #884