Draft: build: Fix error with meson 0.59.0

meson --prefix=/usr --bindir=/usr/aarch64-unknown-linux-gnueabi/bin --sbindir=/usr/aarch64-unknown-linux-gnueabi/bin --libdir=/usr/aarch64-unknown-linux-gnueabi/lib --libexecdir=/usr/aarch64-unknown-linux-gnueabi/libexec --includedir=/usr/aarch64-unknown-linux-gnueabi/include --sysconfdir=/etc --datadir=/usr/share --mandir=/usr/share/man --default-library=shared --native-file meson-native.txt --wrap-mode=nodownload -Dgtk=true -Dintrospection=false -Dgtk_doc=false /mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/gcr-3.40.0
The Meson build system
Version: 0.59.0
Source dir: /mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/gcr-3.40.0
Build dir: /mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/_build
Build type: native build
Project name: gcr
Project version: 3.40.0
C compiler for the host machine: aarch64-unknown-linux-gnueabi-cc (gcc 10.3.0 "aarch64-unknown-linux-gnueabi-gcc (GCC) 10.3.0")
C linker for the host machine: aarch64-unknown-linux-gnueabi-cc ld.bfd 2.36.1
Host machine cpu family: aarch64
Host machine cpu: aarch64
Found pkg-config: /usr/bin/aarch64-unknown-linux-gnueabi-pkg-config (0.29.2)
Run-time dependency glib-2.0 found: YES 2.68.3
Run-time dependency gmodule-no-export-2.0 found: YES 2.68.3
Run-time dependency gthread-2.0 found: YES 2.68.3
Run-time dependency gobject-2.0 found: YES 2.68.3
Run-time dependency gio-2.0 found: YES 2.68.3
Run-time dependency gio-unix-2.0 found: YES 2.68.3
Program gpg found: YES (/usr/bin/gpg)
Run-time dependency libgcrypt found: YES 1.9.3
Run-time dependency p11-kit-1 found: YES 0.23.22
Run-time dependency gtk+-3.0 found: YES 3.24.29
Has header "locale.h" : YES
Checking for function "timegm" : YES
Checking for function "mlock" : YES
Configuring config.h using configuration
Configuring gck-version.h using configuration
Program glib-mkenums found: YES (/usr/bin/glib-mkenums)
Program glib-mkenums found: YES (/usr/bin/glib-mkenums)
Found pkg-config: /usr/bin/aarch64-unknown-linux-gnueabi-pkg-config (0.29.2)
Program glib-genmarshal found: YES (/usr/bin/glib-genmarshal)
Compiler for C supports link arguments -Wl,--version-script,/mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/gcr-3.40.0/gck/libgck.map: YES
Configuring gcr-version.h using configuration
Program glib-mkenums found: YES (/usr/bin/glib-mkenums)
Program glib-mkenums found: YES (/usr/bin/glib-mkenums)
Program glib-genmarshal found: YES (/usr/bin/glib-genmarshal)
Program gdbus-codegen found: YES (/usr/bin/gdbus-codegen)
Program gcr-mkoids found: YES (/bin/sh /mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/gcr-3.40.0/gcr/gcr-mkoids)
Compiler for C supports link arguments -Wl,--version-script,/mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/gcr-3.40.0/gcr/libgcr-base.map: YES
Configuring org.gnome.keyring.SystemPrompter.service using configuration
Configuring org.gnome.keyring.PrivatePrompter.service using configuration
Program glib-compile-schemas found: YES (/usr/bin/glib-compile-schemas)
Program glib-mkenums found: YES (/usr/bin/glib-mkenums)
Program glib-mkenums found: YES (/usr/bin/glib-mkenums)
Compiler for C supports link arguments -Wl,--version-script,/mnt/nvme/builddir/gnome-desktop-gcr-3.40.0/work/gcr-3.40.0/ui/libgcr-ui.map: YES
WARNING: Already generated a pkg-config file for gcr-ui-3
Configuring gcr-viewer.desktop.in using configuration
Configuring gcr-prompter.desktop.in using configuration

../gcr-3.40.0/ui/meson.build:225:5: ERROR: Tried to create target "@BASENAME@_merge", but a target of that name already exists.

I marked this as draft, because I'm not really sure if it needs to be fixed on gcr's or meson's side. Or what exactly changed in meson's behaviour that caused this to result in an error now. So this is more of an RFC to find out how to fix it properly