[OpenMP] Enable warning about "implicit fallthrough"

[Hahnfeld]

Summary

Fix last warned location in ittnotify_static.cpp using the defined
macro KMP_FALLTHROUGH().

[jdoerfert]

thanks! LGTM

[Hahnfeld]

Rebase.

openmp/cmake/HandleOpenMPOptions.cmake

 endif()
 if (OPENMP_ENABLE_WERROR)
   append_if(OPENMP_HAVE_WERROR_FLAG "-Werror" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 endif()
 
 # Additional warnings that are not enabled by -Wall.
 append_if(OPENMP_HAVE_WCAST_QUAL_FLAG "-Wcast-qual" CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WFORMAT_PEDANTIC_FLAG "-Wformat-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
+append_if(OPENMP_HAVE_WIMPLICIT_FALLTHROUGH_FLAG "-Wimplicit-fallthrough" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WSIGN_COMPARE_FLAG "-Wsign-compare" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
 # Warnings that we want to disable because they are too verbose or fragile.
 append_if(OPENMP_HAVE_WNO_EXTRA_FLAG "-Wno-extra" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WNO_PEDANTIC_FLAG "-Wno-pedantic" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 append_if(OPENMP_HAVE_WNO_MAYBE_UNINITIALIZED_FLAG "-Wno-maybe-uninitialized" CMAKE_C_FLAGS CMAKE_CXX_FLAGS)
 
 append_if(OPENMP_HAVE_STD_GNUPP11_FLAG "-std=gnu++11" CMAKE_CXX_FLAGS)
 if (NOT OPENMP_HAVE_STD_GNUPP11_FLAG)
   append_if(OPENMP_HAVE_STD_CPP11_FLAG "-std=c++11" CMAKE_CXX_FLAGS)
 endif()

openmp/cmake/config-ix.cmake

 include(CheckCCompilerFlag)
 include(CheckCXXCompilerFlag)
 
 check_c_compiler_flag(-Wall OPENMP_HAVE_WALL_FLAG)
 check_c_compiler_flag(-Werror OPENMP_HAVE_WERROR_FLAG)
 
 # Additional warnings that are not enabled by -Wall.
 check_cxx_compiler_flag(-Wcast-qual OPENMP_HAVE_WCAST_QUAL_FLAG)
 check_c_compiler_flag(-Wformat-pedantic OPENMP_HAVE_WFORMAT_PEDANTIC_FLAG)
+check_c_compiler_flag(-Wimplicit-fallthrough OPENMP_HAVE_WIMPLICIT_FALLTHROUGH_FLAG)
 check_c_compiler_flag(-Wsign-compare OPENMP_HAVE_WSIGN_COMPARE_FLAG)
 
 # Warnings that we want to disable because they are too verbose or fragile.
 check_c_compiler_flag(-Wno-extra OPENMP_HAVE_WNO_EXTRA_FLAG)
 check_c_compiler_flag(-Wno-pedantic OPENMP_HAVE_WNO_PEDANTIC_FLAG)
 check_c_compiler_flag(-Wno-maybe-uninitialized OPENMP_HAVE_WNO_MAYBE_UNINITIALIZED_FLAG)
 
 check_cxx_compiler_flag(-std=gnu++11 OPENMP_HAVE_STD_GNUPP11_FLAG)
 check_cxx_compiler_flag(-std=c++11 OPENMP_HAVE_STD_CPP11_FLAG)

openmp/runtime/cmake/LibompHandleFlags.cmake

 # C++ compiler flags
 function(libomp_get_cxxflags cxxflags)
   set(flags_local)
   libomp_append(flags_local -fno-exceptions LIBOMP_HAVE_FNO_EXCEPTIONS_FLAG)
   libomp_append(flags_local -fno-rtti LIBOMP_HAVE_FNO_RTTI_FLAG)
   libomp_append(flags_local -Wno-class-memaccess LIBOMP_HAVE_WNO_CLASS_MEMACCESS_FLAG)
   libomp_append(flags_local -Wno-covered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
   libomp_append(flags_local -Wno-frame-address LIBOMP_HAVE_WNO_FRAME_ADDRESS_FLAG)
-  libomp_append(flags_local -Wno-implicit-fallthrough LIBOMP_HAVE_WNO_IMPLICIT_FALLTHROUGH_FLAG)
   libomp_append(flags_local -Wno-strict-aliasing LIBOMP_HAVE_WNO_STRICT_ALIASING_FLAG)
   libomp_append(flags_local -Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
   libomp_append(flags_local -Wno-stringop-truncation LIBOMP_HAVE_WNO_STRINGOP_TRUNCATION_FLAG)
   libomp_append(flags_local -Wno-switch LIBOMP_HAVE_WNO_SWITCH_FLAG)
   libomp_append(flags_local -Wno-unused-but-set-variable LIBOMP_HAVE_WNO_UNUSED_BUT_SET_VARIABLE_FLAG)
   libomp_append(flags_local /GS LIBOMP_HAVE_GS_FLAG)
   libomp_append(flags_local /EHsc LIBOMP_HAVE_EHSC_FLAG)
   libomp_append(flags_local /Oy- LIBOMP_HAVE_OY__FLAG)

openmp/runtime/cmake/config-ix.cmake

 endfunction()
 
 # Checking CXX, Linker Flags
 check_cxx_compiler_flag(-fno-exceptions LIBOMP_HAVE_FNO_EXCEPTIONS_FLAG)
 check_cxx_compiler_flag(-fno-rtti LIBOMP_HAVE_FNO_RTTI_FLAG)
 check_cxx_compiler_flag(-Wno-class-memaccess LIBOMP_HAVE_WNO_CLASS_MEMACCESS_FLAG)
 check_cxx_compiler_flag(-Wno-covered-switch-default LIBOMP_HAVE_WNO_COVERED_SWITCH_DEFAULT_FLAG)
 check_cxx_compiler_flag(-Wno-frame-address LIBOMP_HAVE_WNO_FRAME_ADDRESS_FLAG)
-check_cxx_compiler_flag(-Wno-implicit-fallthrough LIBOMP_HAVE_WNO_IMPLICIT_FALLTHROUGH_FLAG)
 check_cxx_compiler_flag(-Wno-strict-aliasing LIBOMP_HAVE_WNO_STRICT_ALIASING_FLAG)
 check_cxx_compiler_flag(-Wstringop-overflow=0 LIBOMP_HAVE_WSTRINGOP_OVERFLOW_FLAG)
 check_cxx_compiler_flag(-Wno-stringop-truncation LIBOMP_HAVE_WNO_STRINGOP_TRUNCATION_FLAG)
 check_cxx_compiler_flag(-Wno-switch LIBOMP_HAVE_WNO_SWITCH_FLAG)
 check_cxx_compiler_flag(-Wno-uninitialized LIBOMP_HAVE_WNO_UNINITIALIZED_FLAG)
 check_cxx_compiler_flag(-Wno-unused-but-set-variable LIBOMP_HAVE_WNO_UNUSED_BUT_SET_VARIABLE_FLAG)
 check_cxx_compiler_flag(-msse2 LIBOMP_HAVE_MSSE2_FLAG)
 check_cxx_compiler_flag(-ftls-model=initial-exec LIBOMP_HAVE_FTLS_MODEL_FLAG)

openmp/runtime/src/thirdparty/ittnotify/ittnotify_static.cpp

 
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "kmp_config.h"
+#include "kmp_os.h"
 #include "ittnotify_config.h"
 
 #if ITT_PLATFORM==ITT_PLATFORM_WIN
 #if defined(__MINGW32__)
 #include <limits.h>
 #else
 #define PATH_MAX 512
 #endif
#endif /* ITT_SIMPLE_INIT */
                     if (_N_(_ittapi_global).lib != NULL)
                     {
                         __itt_api_init_t* __itt_api_init_ptr;
                         int lib_version = __itt_lib_version(_N_(_ittapi_global).lib);
 
                         switch (lib_version) {
                         case 0:
                             groups = __itt_group_legacy;
+                            KMP_FALLTHROUGH();
                         case 1:
                             /* Fill all pointers from dynamic library */
                             for (i = 0; _N_(_ittapi_global).api_list_ptr[i].name != NULL; i++)
                             {
                                 if (_N_(_ittapi_global).api_list_ptr[i].group & groups & init_groups)
                                 {
                                     *_N_(_ittapi_global).api_list_ptr[i].func_ptr = (void*)__itt_get_proc(_N_(_ittapi_global).lib, _N_(_ittapi_global).api_list_ptr[i].name);
                                     if (*_N_(_ittapi_global).api_list_ptr[i].func_ptr == NULL)