LD_PRELOAD is supported on OpenBSD

Index: meson.build
--- meson.build.orig
+++ meson.build
@@ -780,7 +780,7 @@ if not ['x86', 'x86_64'].contains(host_machine.cpu_fam
   conf.set('ATOMIC_OP_NEEDS_MEMORY_BARRIER', 1)
 endif
 
-have_ld_preload = ['linux', 'freebsd', 'darwin', 'dragonfly'].contains(host_machine.system())
+have_ld_preload = ['linux', 'freebsd', 'darwin', 'dragonfly', 'openbsd'].contains(host_machine.system())
 
 if have_ld_preload and zlib_dep.found() and conf.get('CAIRO_HAS_REAL_PTHREAD', 0) == 1 and conf.get('CAIRO_HAS_DLSYM', 0) == 1
   conf.set('CAIRO_HAS_TRACE', 1)