devel/tigcc: Unbreak build with GCC 9

.../gnu/gcc-4.1-20060728/gcc/c-decl.c: At top level:
.../gnu/gcc-4.1-20060728/gcc/c-decl.c:1130:1: error: 'cgraph_node' is not defined as a type
1130 | locate_old_decl (tree decl, void (*diag)(const char *, ...) ATTRIBUTE_GCC_CDIAG(1,2))

| ^~~~~~~~~~~~~~~

http://pb2.nyi.freebsd.org/data/120i386-default-PR238330/2019-06-09_20h27m22s/logs/errors/tigcc-0.96.b8_9.log

Workaround for https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90677

PR: 238330