Fix rpc test Makefile

Signed-off-by: Carmelo Amoroso <carmelo.amoroso@st.com>

test/rpc/Makefile

@@ -3,6 +3,10 @@
 
 TESTS := getrpcent
 
+ifeq ($(UCLIBC_HAS_REENTRANT_RPC),y)
+TESTS += getrpcent_r
+endif
+
 include ../Test.mak
 
 DODIFF_getrpcent := 1