$ ../cpla.sh  p178
$ clang++ p178.cpp -std=c++03 -Wall
p178.cpp:12:2: error: expected expression
[[maybe_unused]] void f([[maybe_unused]] bool thing1,
 ^
p1798.cpp:12:18: error: expected unqualified-id
[[maybe_unused]] void f([[maybe_unused]] bool thing1,
                 ^
p178.cpp:21:3: error: use of undeclared identifier 'f'
  f(a,b);
  ^
3 errors generated.
$ clang++ p178.cpp -std=c++2a -Wall
b=1
C++N4741(96)10.6.6 Maybe unused attribute [dcl.attr.unused]p178.cpp

$ g++-8 p178.cpp -std=c++03  -Wall
p178.cpp:12:1: error: expected unqualified-id before '[' token
 [[maybe_unused]] void f([[maybe_unused]] bool thing1,
 ^
p178.cpp: In function 'int main()':
p178.cpp:21:3: error: 'f' was not declared in this scope
   f(a,b);
   ^

$ g++-8 p178.cpp -std=c++2a  -Wall
b=1
C++N4741(96)10.6.7 Maybe unused attribute [dcl.attr.unused]p178.cpp