gcc: ada: delete old $(P) reference

The P variable was deleted back in Nov 2015 (svn rev 231062),
but its expansion was missed.  Delete those now too.

From-SVN: r250307

gcc/ada/ChangeLog

+2017-07-18  Mike Frysinger  <vapier@chromium.org>
+
+	* gcc-interface/Makefile.in ($(P)): Delete
+
 2017-07-15  John Paul Adrian Glaubitz  <glaubitz@physik.fu-berlin.de>
 
 	PR ada/81446

gcc/ada/gcc-interface/Makefile.in

@@ -2643,10 +2643,10 @@ gnatlink-re: ../stamp-tools gnatmake-re
 #  stamp target in the parent directory whenever gnat1 is rebuilt
 
 # Likewise for the tools
-../../gnatmake$(exeext): $(P) b_gnatm.o $(GNATMAKE_OBJS)
+../../gnatmake$(exeext): b_gnatm.o $(GNATMAKE_OBJS)
 	+$(GCC_LINK) $(ALL_CFLAGS) -o $@ b_gnatm.o $(GNATMAKE_OBJS) $(TOOLS_LIBS) $(TOOLS1_LIBS)
 
-../../gnatlink$(exeext): $(P) b_gnatl.o $(GNATLINK_OBJS)
+../../gnatlink$(exeext): b_gnatl.o $(GNATLINK_OBJS)
 	+$(GCC_LINK) $(ALL_CFLAGS) -o $@ b_gnatl.o $(GNATLINK_OBJS) $(TOOLS_LIBS) $(TOOLS1_LIBS)
 
 ../stamp-gnatlib-$(RTSDIR):