Compilation failed for compile-pentium64-gcov script if gcc < 7

$ gcc --version

gcc (Ubuntu 6.5.0-2ubuntu1~18.04) 6.5.0 20181026

Copyright (C) 2017 Free Software Foundation, Inc.

This is free software; see the source for copying conditions.  There is NO

warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

$ ./BUILD/compile-pentium64-gcov

testing k6 ... ok

./BUILD/compile-pentium64-gcov=> : path=./BUILD

./BUILD/compile-pentium64-gcov=> : . ./BUILD/autorun.sh

./BUILD/compile-pentium64-gcov=> : dirname ./BUILD/compile-pentium64-gcov

./BUILD/compile-pentium64-gcov=> : path=./BUILD

./BUILD/compile-pentium64-gcov=> : cp ./BUILD/cmake_configure.sh ./BUILD/../configure

./BUILD/compile-pentium64-gcov=> : chmod +x ./BUILD/../configure

./BUILD/compile-pentium64-gcov=> : git submodule update

./BUILD/compile-pentium64-gcov=> : CC=gcc CFLAGS=-Wall -Wextra -Wunused -Wwrite-strings -Wno-uninitialized -Wno-strict-aliasing -Wimplicit-fallthrough=2 -Wformat-security -Wvla  -mtune=native -m64  -fprofile-arcs -ftest-coverage -DDISABLE_TAO_ASM -DMYSQL_SERVER_SUFFIX=-gcov -DHAVE_gcov   CXX=g++ CXXFLAGS=-Wall -Wextra -Wunused -Wwrite-strings -Wno-uninitialized -Wno-strict-aliasing -Wimplicit-fallthrough=2 -Wformat-security -Wvla -Wno-unused-parameter -Wno-invalid-offsetof -Wnon-virtual-dtor  -felide-constructors -fexceptions -mtune=native -m64  -fprofile-arcs -ftest-coverage -DDISABLE_TAO_ASM -DMYSQL_SERVER_SUFFIX=-gcov -DHAVE_gcov   CXXLDFLAGS= ./configure --prefix=/usr/local/mysql --enable-assembler --with-extra-charsets=complex --enable-thread-safe-client --with-big-tables --with-plugin-aria --with-aria-tmp-tables --with-plugin-s3=STATIC --with-debug --with-gcov --with-ssl --with-plugins=max --with-embedded-server --with-libevent --with-plugin-rocksdb=dynamic --with-plugin-test_sql_discovery=DYNAMIC --with-plugin-file_key_management=DYNAMIC --without-oqgraph --enable-local-infile

configure.pl : calling cmake /home/anel/mariadb/10.6  -DCMAKE_INSTALL_PREFIX=/usr/local/mysql -DENABLE_ASSEMBLER=1 -DWITH_EXTRA_CHARSETS=complex -DENABLE_THREAD_SAFE_CLIENT=1 -DWITH_BIG_TABLES=1 -DWITH_PLUGIN_ARIA=1 -DWITH_ARIA_TMP_TABLES=1 -DPLUGIN_S3=STATIC -DCMAKE_BUILD_TYPE=Debug -DSECURITY_HARDENED=OFF -DENABLE_GCOV=ON -DWITH_SSL=bundled -DWITH_MAX=AUTO -DWITH_EMBEDDED_SERVER=1 -DWITH_LIBEVENT=bundled -DPLUGIN_ROCKSDB=DYNAMIC -DPLUGIN_TEST_SQL_DISCOVERY=DYNAMIC -DPLUGIN_FILE_KEY_MANAGEMENT=DYNAMIC -DWITHOUT_OQGRAPH=1 -DENABLE_LOCAL_INFILE=1

-- The C compiler identification is GNU 6.5.0

-- The CXX compiler identification is GNU 6.5.0

-- Detecting C compiler ABI info

-- Detecting C compiler ABI info - failed

-- Check for working C compiler: /usr/bin/gcc

-- Check for working C compiler: /usr/bin/gcc - broken

CMake Error at /usr/local/share/cmake-3.20/Modules/CMakeTestCCompiler.cmake:66 (message):

  The C compiler

    "/usr/bin/gcc"

  is not able to compile a simple test program.

  It fails with the following output:

    Change Dir: /home/anel/mariadb/10.6/CMakeFiles/CMakeTmp

    Run Build Command(s):/usr/bin/make -f Makefile cmTC_5749f/fast && /usr/bin/make  -f CMakeFiles/cmTC_5749f.dir/build.make CMakeFiles/cmTC_5749f.dir/build

    make[1]: Entering directory '/home/anel/mariadb/10.6/CMakeFiles/CMakeTmp'

    Building C object CMakeFiles/cmTC_5749f.dir/testCCompiler.c.o

    /usr/bin/gcc   -Wall -Wextra -Wunused -Wwrite-strings -Wno-uninitialized -Wno-strict-aliasing -Wimplicit-fallthrough=2 -Wformat-security -Wvla  -mtune=native -m64  -fprofile-arcs -ftest-coverage -DDISABLE_TAO_ASM -DMYSQL_SERVER_SUFFIX=-gcov -DHAVE_gcov  -o CMakeFiles/cmTC_5749f.dir/testCCompiler.c.o -c /home/anel/mariadb/10.6/CMakeFiles/CMakeTmp/testCCompiler.c

    gcc: error: unrecognized command line option ‘-Wimplicit-fallthrough=2’; did you mean ‘-Wno-fallthrough’?

    CMakeFiles/cmTC_5749f.dir/build.make:77: recipe for target 'CMakeFiles/cmTC_5749f.dir/testCCompiler.c.o' failed

    make[1]: *** [CMakeFiles/cmTC_5749f.dir/testCCompiler.c.o] Error 1

    make[1]: Leaving directory '/home/anel/mariadb/10.6/CMakeFiles/CMakeTmp'

    Makefile:127: recipe for target 'cmTC_5749f/fast' failed

    make: *** [cmTC_5749f/fast] Error 2

  CMake will not be able to correctly generate this project.

Call Stack (most recent call first):

  CMakeLists.txt:30 (PROJECT)

-- Configuring incomplete, errors occurred!

See also "/home/anel/mariadb/10.6/CMakeFiles/CMakeOutput.log".

See also "/home/anel/mariadb/10.6/CMakeFiles/CMakeError.log".

./BUILD/compile-pentium64-gcov=> : make -j 6

make: *** No targets specified and no makefile found.  Stop.