Reuse c_compile rule in C unit test suite makefile

No real changes, just reuse the commands defined in the C section of the top
level Examples/Makefile instead of (imperfectly, i.e. CFLAGS was forgotten
here) duplicating them in Examples/test-suite/c/Makefile.

Examples/Makefile.in

@@ -1749,7 +1749,7 @@ c_cpp: $(SRCDIR_SRCS)
 	$(SYNTAX_CHECK) -I$(SRCDIR)$(INTERFACEDIR) $(IWRAP:.i=.h)
 
 c_compile: $(SRCDIR)$(RUNME).c
-	$(COMPILETOOL) $(CC) $(CFLAGS) -o $(RUNME) -I. $< -L. -l$(TARGET)
+	$(COMPILETOOL) $(CC) $(CFLAGS) -o $(RUNME) -I. -I.. $< -L. -l$(TARGET)
 
 # -----------------------------------------------------------------
 # Run C example

Examples/test-suite/c/Makefile.in

@@ -229,10 +229,13 @@ setup = \
 # Compiles C files then runs the testcase. A testcase is only run if
 # a file is found which has _runme.c appended after the testcase name.
 run_testcase = \
-	if [ -f $(srcdir)/$(SCRIPTPREFIX)$*$(SCRIPTSUFFIX) ]; then (\
-		cd $* && $(COMPILETOOL) $(CC) ../$(srcdir)/$(SCRIPTPREFIX)$*$(SCRIPTSUFFIX) -I.. -L. -l$* -o $*_runme && \
-	  env LD_LIBRARY_PATH=".:$$LD_LIBRARY_PATH" PATH=".:$$PATH" SHLIB_PATH=".:$$SHLIB_PATH" DYLD_LIBRARY_PATH=".:$$DYLD_LIBRARY_PATH" $(RUNTOOL) ./$*_runme;) \
-	fi;
+	+if [ -f $(srcdir)/$(SCRIPTPREFIX)$*$(SCRIPTSUFFIX) ]; then \
+	  cd $* && $(MAKE) -f $(top_builddir)/$(EXAMPLES)/Makefile \
+	    SRCDIR='$(SRCDIR)' \
+	    RUNME=$*_runme \
+	    TARGET='$*' \
+	    c_run; \
+	fi
 
 # Clean: remove testcase directories
 %.clean: