C++ shared or static library 'absl_flags_registry' not found - when building webrtc-audio-processing

### Describe the issue

I was trying to compile the new release of « webrtc-audio-processing » which can be found [here](https://www.freedesktop.org/software/pulseaudio/webrtc-audio-processing/), it runned good until i had this message :

```
The Meson build system
Version: 0.59.4
Source dir: /tmp/SBo/webrtc-audio-processing-1.0
Build dir: /tmp/SBo/webrtc-audio-processing-1.0/build
Build type: native build
Project name: webrtc-audio-processing-1
Project version: 1.0
C compiler for the host machine: ccache cc (gcc 11.2.0 "cc (GCC) 11.2.0")
C linker for the host machine: cc ld.bfd 2.37-slack15
C++ compiler for the host machine: ccache c++ (gcc 11.2.0 "c++ (GCC) 11.2.0")
C++ linker for the host machine: c++ ld.bfd 2.37-slack15
Host machine cpu family: x86_64
Host machine cpu: x86_64
Library absl_base found: YES
Library absl_bad_optional_access found: YES
Library absl_flags_internal found: YES
Library absl_flags_marshalling found: YES
Library absl_flags_parse found: YES

../meson.build:43:0: ERROR: C++ shared or static library 'absl_flags_registry' not found
```
So, is this a problem related to the new release of abseil-cpp, or must I look at the WebRTC side ?

### Steps to reproduce the problem

Here's the piece of code from my webrtc-audio-processing.SlackBuild :

```
mkdir build
cd build
CFLAGS="$SLKCFLAGS" \
CXXFLAGS="$SLKCFLAGS" \
meson .. \
--buildtype=release \
--infodir=/usr/info \
--libdir=/usr/lib${LIBDIRSUFFIX} \
--localstatedir=/var \
--mandir=/usr/man \
--prefix=/usr \
--sysconfdir=/etc \
-Dstrip=true
"${NINJA:=ninja}"
DESTDIR=$PKG $NINJA install
cd ..

```

### What version of Abseil are you using?

Abseil LTS 20230125

### What operating system and version are you using?

GNU/Linux Slackware64 15.0

### What compiler and version are you using?

gcc version 11.2.0

```
Reading specs from /usr/lib64/gcc/x86_64-slackware-linux/11.2.0/specs
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-slackware-linux/11.2.0/lto-wrapper
Target: x86_64-slackware-linux
Configured with: ../gcc-11.2.0/configure --prefix=/usr --libdir=/usr/lib64 --mandir=/usr/man --infodir=/usr/info --enable-shared --enable-bootstrap --enable-languages=ada,brig,c,c++,d,fortran,go,lto,objc,obj-c++ --enable-threads=posix --enable-checking=release --enable-objc-gc --with-system-zlib --enable-libstdcxx-dual-abi --with-default-libstdcxx-abi=new --disable-libstdcxx-pch --disable-libunwind-exceptions --enable-__cxa_atexit --disable-libssp --enable-gnu-unique-object --enable-plugin --enable-lto --disable-install-libiberty --enable-gnu-indirect-function --with-linker-hash-style=gnu --with-gnu-ld --with-isl --verbose --with-arch-directory=amd64 --disable-gtktest --disable-werror --enable-clocale=gnu --enable-multilib --target=x86_64-slackware-linux --build=x86_64-slackware-linux --host=x86_64-slackware-linux
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.2.0 (GCC)
```

### What build system are you using?

cmake version 3.21.4

### Additional context

So it's whether an Abseil problem, so a WebRTC problem, for the moment i don't know. I managed to build WebRTC 0.1 with and old script i found (2011 !) but we're now on 1.0.

Thanks for your help and patience,

Chris