Looks like LDAP-related commit http://git.claws-mail.org/?p=claws.git;a=commit;h=48f72c22f91fbe0d6e872e89bd4dce9d39090e81 breaks the claws-mail build from GIT master on arch linux:
[...]
compose.c: In function ‘_ldap_srv_func’:
compose.c:7100:2: error: unknown type name ‘LdapServer’; did you mean ‘GDBusServer’?
  LdapServer *server = (LdapServer *)data;
  ^~~~~~~~~~
  GDBusServer
compose.c:7100:24: error: ‘LdapServer’ undeclared (first use in this function); did you mean ‘server’?
  LdapServer *server = (LdapServer *)data;
                        ^~~~~~~~~~
                        server
compose.c:7100:24: note: each undeclared identifier is reported only once for each function it appears in
compose.c:7100:36: error: expected expression before ‘)’ token
  LdapServer *server = (LdapServer *)data;
                                    ^
compose.c:7103:86: error: request for member ‘control’ in something not a structure or union
  debug_print("%s server '%s'\n", (*enable == TRUE ? "enabling" : "disabling"), server->control->hostName);
                                                                                      ^~
compose.c:7104:8: error: request for member ‘searchFlag’ in something not a structure or union
  server->searchFlag = *enable;
        ^~
compose.c: In function ‘compose_destroy’:
compose.c:9102:25: error: ‘Compose {aka struct _Compose}’ has no member named ‘passworded_ldap_servers’
  g_slist_foreach(compose->passworded_ldap_servers,
                         ^~
compose.c:9104:22: error: ‘Compose {aka struct _Compose}’ has no member named ‘passworded_ldap_servers’
  g_slist_free(compose->passworded_ldap_servers);
                      ^~
make[4]: *** [Makefile:1492: compose.o] Error 1
make[4]: Leaving directory '/home/glitsj16/.buildzone/00.tmpfs/claws/src'
make[3]: *** [Makefile:1552: all-recursive] Error 1
make[3]: Leaving directory '/home/glitsj16/.buildzone/00.tmpfs/claws/src'
make[2]: *** [Makefile:1241: all] Error 2
make[2]: Leaving directory '/home/glitsj16/.buildzone/00.tmpfs/claws/src'
make[1]: *** [Makefile:775: all-recursive] Error 1
make[1]: Leaving directory '/home/glitsj16/.buildzone/00.tmpfs/claws'
make: *** [Makefile:550: all] Error 2

Full log at https://ptpb.pw/rx0v.debug
When reverting the aforementioned commit the build goes fine.

Regards