GCC 7, -Wimplicit-fallthrough warnings, and portable way to clear them?

We are catching warnings from GCC 7 for implicit fall through in a switch statement. Previously, we cleared them under Clang (that's the reason for the comment seen below):

g++ -DNDEBUG -g2 -O3 -std=c++17 -Wall -Wextra -fPIC -c authenc.cppasn.cpp: In member function ‘void EncodedObjectFilter::Put(const byte*, size_t)’:asn.cpp:359:18: warning: this statement may fall through [-Wimplicit-fallthrough=]    m_state = BODY;  // fall through                  ^asn.cpp:361:3: note: here   case BODY:   ^~~~

The GCC manual states to use __attribute__ ((fallthrough)), but its not portable. The manual also states "... it is also possible to add a fallthrough comment to silence the warning", but it only offer FALLTHRU (is this really the only choice?):

switch (cond)  {  case 1:    bar (0);    /* FALLTHRU */  default:…  }

Is there a portable way to clear the fall through warning for both Clang and GCC? If so, then what is it?