The build fails with a strict C99 compiler:

gcc -Isubprojects/mocklibc-1.0/src/mocklibc-debug-netgroup.p -Isubprojects/mocklibc-1.0/src -I../subprojects/mocklibc-1.0/src -fdiagnostics-color=always -D_FILE_OFFSET_BITS=64 -Wall -Winvalid-pch -O2 -flto=auto -ffat-lto-objects -fexceptions -g -grecord-gcc-switches -pipe -Wall -Werror=format-security -Wp,-U_FORTIFY_SOURCE,-D_FORTIFY_SOURCE=3 -Wp,-D_GLIBCXX_ASSERTIONS -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -fstack-protector-strong -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -fno-omit-frame-pointer -mno-omit-leaf-frame-pointer -MD -MQ subprojects/mocklibc-1.0/src/mocklibc-debug-netgroup.p/netgroup-debug.c.o -MF subprojects/mocklibc-1.0/src/mocklibc-debug-netgroup.p/netgroup-debug.c.o.d -o subprojects/mocklibc-1.0/src/mocklibc-debug-netgroup.p/netgroup-debug.c.o -c ../subprojects/mocklibc-1.0/src/netgroup-debug.c
../subprojects/mocklibc-1.0/src/netgroup-debug.c: In function ‘netgroup_debug_print_entry’:
../subprojects/mocklibc-1.0/src/netgroup-debug.c:25:3: error: implicit declaration of function ‘print_indent’
   25 |   print_indent(stream, indent);
      |   ^~~~~~~~~~~~

This is the same issue that was reported here: <https://code.google.com/archive/p/mocklibc/issues/3> But Google seems to have deleted the patch.

I don't know how to integrate a fix into the meson build system that accountsservice uses.