nptl: Fix nptl specific case which still was not using CSRC-y.

Signed-off-by: Khem Raj <raj.khem@gmail.com>

libc/signal/Makefile.in

@@ -17,7 +17,7 @@ CSRC-$(UCLIBC_HAS_OBSOLETE_SYSV_SIGNAL) += sysv_signal.c
 CSRC-$(UCLIBC_SUSV4_LEGACY) += sigintr.c
 
 ifeq ($(UCLIBC_HAS_THREADS_NATIVE),y)
-CSRC:=$(filter-out raise.c sigaction.c,$(CSRC))
+CSRC-y:=$(filter-out raise.c sigaction.c,$(CSRC-y))
 endif
 
 ifneq ($(strip $(ARCH_OBJS)),)