tools build: Add test for missing include

The current build framework fails to cope with header file removal. The
reason is that the removed header file stays in the .cmd file target
rule and forces the build to fail.

This issue is fixed and explained in the following patches.

Adding a new build test that simulates header removal.

Signed-off-by: Jiri Olsa <[e-mail]>
Cc: David Ahern <[e-mail]>
Cc: Namhyung Kim <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/build/tests/ex/Build

···
 ex-y += b.o
 ex-y += empty/
 ex-y += empty2/
+ex-y += inc.o
 
 libex-y += c.o
 libex-y += d.o

tools/build/tests/ex/Makefile

···
-export srctree := ../../../..
+export srctree := $(abspath ../../../..)
 export CC      := gcc
 export LD      := ld
 export AR      := ar

tools/build/tests/ex/ex.c

···
 int d(void);
 int e(void);
 int f(void);
+int inc(void);
 
 int main(void)
 {
···
 	d();
 	e();
 	f();
+	inc();
 
 	return 0;
 }

tools/build/tests/ex/inc.c

···
+#ifdef INCLUDE
+#include "krava.h"
+#endif
+
+int inc(void)
+{
+	return 0;
+}

tools/build/tests/run.sh

···
 	make -C ex V=1 clean > /dev/null 2>&1
 	rm -f ex.out
 }
+
+function test_ex_include {
+	make -C ex V=1 clean > ex.out 2>&1
+
+	# build with krava.h include
+	touch ex/krava.h
+	make -C ex V=1 CFLAGS=-DINCLUDE >> ex.out 2>&1
+
+	if [ ! -x ./ex/ex ]; then
+	  echo FAILED
+	  exit -1
+	fi
+
+	# build without the include
+	rm -f ex/krava.h ex/ex
+	make -C ex V=1 >> ex.out 2>&1
+
+	if [ ! -x ./ex/ex ]; then
+	  echo FAILED
+	  exit -1
+	fi
+
+	make -C ex V=1 clean > /dev/null 2>&1
+	rm -f ex.out
+}
+
 echo -n Testing..
 
 test_ex
 test_ex_suffix
+test_ex_include
 
 echo OK