MEDIUM: mworker: get rid of libsystemd

MEDIUM: mworker: get rid of libsystemd

Given the xz drama which allowed liblzma to be linked to openssh, lets remove
libsystemd to get rid of useless dependencies.

The sd_notify API seems to be stable and is now documented. This patch replaces
the sd_notify() and sd_notifyf() function by a reimplementation inspired by the
systemd documentation.

This should not change anything functionnally. The function will be built when
haproxy is built using USE_SYSTEMD=1.

References:
  https://github.com/systemd/systemd/issues/32028
  https://www.freedesktop.org/software/systemd/man/devel/sd_notify.html#Notes

Before:

wla@kikyo:~% ldd /usr/sbin/haproxy
	linux-vdso.so.1 (0x00007ffcfaf65000)
	libcrypt.so.1 => /lib/x86_64-linux-gnu/libcrypt.so.1 (0x000074637fef4000)
	libssl.so.3 => /lib/x86_64-linux-gnu/libssl.so.3 (0x000074637fe4f000)
	libcrypto.so.3 => /lib/x86_64-linux-gnu/libcrypto.so.3 (0x000074637f400000)
	liblua5.4.so.0 => /lib/x86_64-linux-gnu/liblua5.4.so.0 (0x000074637fe0d000)
	libsystemd.so.0 => /lib/x86_64-linux-gnu/libsystemd.so.0 (0x000074637f92a000)
	libpcre2-8.so.0 => /lib/x86_64-linux-gnu/libpcre2-8.so.0 (0x000074637f365000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x000074637f000000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x000074637f27a000)
	libcap.so.2 => /lib/x86_64-linux-gnu/libcap.so.2 (0x000074637fdff000)
	libgcrypt.so.20 => /lib/x86_64-linux-gnu/libgcrypt.so.20 (0x000074637eeb8000)
	liblzma.so.5 => /lib/x86_64-linux-gnu/liblzma.so.5 (0x000074637fdcd000)
	libzstd.so.1 => /lib/x86_64-linux-gnu/libzstd.so.1 (0x000074637ee01000)
	liblz4.so.1 => /lib/x86_64-linux-gnu/liblz4.so.1 (0x000074637fda8000)
	/lib64/ld-linux-x86-64.so.2 (0x000074637ff5d000)
	libgpg-error.so.0 => /lib/x86_64-linux-gnu/libgpg-error.so.0 (0x000074637f904000)

After:

wla@kikyo:~% ldd /usr/sbin/haproxy
	linux-vdso.so.1 (0x00007ffd51901000)
	libcrypt.so.1 => /lib/x86_64-linux-gnu/libcrypt.so.1 (0x00007f758d6c0000)
	libssl.so.3 => /lib/x86_64-linux-gnu/libssl.so.3 (0x00007f758d61b000)
	libcrypto.so.3 => /lib/x86_64-linux-gnu/libcrypto.so.3 (0x00007f758ca00000)
	liblua5.4.so.0 => /lib/x86_64-linux-gnu/liblua5.4.so.0 (0x00007f758d5d9000)
	libpcre2-8.so.0 => /lib/x86_64-linux-gnu/libpcre2-8.so.0 (0x00007f758d365000)
	libz.so.1 => /lib/x86_64-linux-gnu/libz.so.1 (0x00007f758d5ba000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007f758c600000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007f758c915000)
	/lib64/ld-linux-x86-64.so.2 (0x00007f758d729000)

A backport to all stable versions could be considered at some point.