CI: Fix C/C++ standard customization

[jimklimov]

While our NUT CI matrix code allows to pick -std=... settings for CFLAGS and CXXFLAGS, it was found that builds launched allegedly in c99/c++98 mode (or gnu equivalents) did not actually use that, and added flags for C11/C++11 (if supported by compiler) regardless.

This PR fixes the detection we have for caller-specified -std=... or -ansi to avoid slapping on another value, and some fallout of this change per CI findings.

NOTE: Builds in strict-C -ansi mode (aka c89 and c++98) do not pass - unable to find many standard library methods and types in system headers (snprintf, timespec etc.) and complain about // comments that remain abundant in our codebase. So they are not a practical immediate goal. However, builds requested with gnu89 and gnu++98 modes (to whatever extent C++ would be or not be enabled in practice) should pass.

[jimklimov]

Now CFLAGS='-ansi' CXXFLAGS='-ansi' ./ci_build.sh passes locally again (on an Ubuntu 22.04.3 LTS VM). NUT config summary:

NUT Configuration summary:

• configured version: 2.8.1.1 (v2.8.1-452-g4d4cf333f)
• build serial drivers: yes
• build USB drivers: yes (libusb-1.0)
• build neon based XML driver: yes
• enable Avahi support: yes
• build Powerman PDU client driver: yes
• build Modbus driver: yes
• build IPMI driver: yes (FreeIPMI)
• build GPIO driver: yes libgpiod
• build Mac OS X meta-driver: no
• build i2c based drivers: yes
• enable SSL support: yes (OpenSSL)
• enable libwrap (tcp-wrappers) support: yes
• enable libltdl (Libtool dlopen abstraction) support: yes
• build nut-scanner: yes
• build CGI programs: yes
• install NUT-Monitor desktop application: no
• install PyNUT binding module: yes
• use default Python interpreter: /usr/bin/python
• use specific Python2 interpreter: /usr/bin/python2
• use specific Python3 interpreter: /usr/bin/python3.10
• build and install documentation: skip
• build specific documentation format(s): no
• build and install the development files: yes
• consider basic SMF support: no
• consider basic systemd support: yes
• build with tighter systemd support: yes
• build C++11 codebase (client library, etc.): no
• build C++ tests with CPPUNIT: no
• build SNMP drivers: yes
• build SNMP drivers with statically linked lib(net)snmp: no
• User to run as: nobody
• Group of user to run as: nogroup

NUT Paths:

• Default installation prefix path: /usr/local/ups
• State file path: /var/state/ups
• Unprivileged PID file path: /var/state/ups
• Privileged PID file path: /run
• Driver program path: /usr/local/ups/bin
• CGI program path: /usr/local/ups/cgi-bin
• HTML file path: /usr/local/ups/html
• Config file path: /usr/local/ups/etc
• Data file path: /usr/local/ups/share
• Tool program path: /usr/local/ups/bin
• System program path: /usr/local/ups/sbin
• System library path: /usr/local/ups/lib
• System exec-library path: /usr/local/ups/libexec

NUT Paths for third-party integrations:

• Default Python interpreter site-packages: /usr/local/lib/python3.10/dist-packages
• Specific Python2 interpreter site-packages: /usr/local/lib/python2.7/dist-packages
• Specific Python3 interpreter site-packages: /usr/local/lib/python3.10/dist-packages
• pkg-config *.pc directory: ${libdir}/pkgconfig => /usr/local/ups/lib/pkgconfig
• Service units for systemd: /lib/systemd/system
• Shutdown hooks for systemd: /lib/systemd/system-shutdown
• Systemd-tmpfiles configs: /usr/lib/tmpfiles.d
• Augeas lenses directory: /usr/share/augeas/lenses/dist
• Udev rules directory: /lib/udev

NUT Build/Target system info:

• Compact version of C compiler: gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
• Compact version of C++ compiler: g++ (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
• Compact version of C preprocessor: gcc (Ubuntu 11.4.0-1ubuntu1~22.04) 11.4.0
• host env spec we run on: x86_64-pc-linux-gnu
• host env spec we built on: x86_64-pc-linux-gnu
• host env spec we built for: x86_64-pc-linux-gnu
• host OS short spec we run on: x86_64-linux-gnu
• host OS short spec we built on: x86_64-linux-gnu
• host OS short spec we built for: x86_64-linux-gnu
• host multiarch spec we build for (as suggested by compiler being used): x86_64-linux-gnu
• ccache namespace tag (if ccache is used and new enough): nut:x86_64-linux-gnu

NUT Compiler settings:

• CC : gcc
• CFLAGS : -isystem /usr/local/include -ansi -Wno-reserved-identifier -fdiagnostics-color=always -Wno-unknown-warning-option -Wall -Wsign-compare -Werror
• CXX : g++
• CXXFLAGS : -isystem /usr/local/include -ansi -Wno-reserved-identifier -fdiagnostics-color=always -Wno-unknown-warning-option -Wall -Wextra -Werror
• CPP : gcc -E
• CPPFLAGS :
• CONFIG_FLAGS : --enable-Wcolor --enable-warnings --enable-Werror --enable-keep_nut_report_feature --with-all=auto --with-cgi=auto --with-serial=auto --with-dev=auto --with-doc=skip --with-nut_monitor=auto --with-pynut=auto --disable-force-nut-version-header --enable-check-NIT --enable-maintainer-mode --disable-silent-rules

[jimklimov]

Ignore the shellcheck fault, CI builder got restarted.