selftests/rseq: Fix out-of-tree compilation

Currently if you build with O=... the rseq tests don't build:

  $ make O=$PWD/output -C tools/testing/selftests/ TARGETS=rseq
  make: Entering directory '/linux/tools/testing/selftests'
  ...
  make[1]: Entering directory '/linux/tools/testing/selftests/rseq'
  gcc -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./  -shared -fPIC rseq.c -lpthread -o /linux/output/rseq/librseq.so
  gcc -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./  basic_test.c -lpthread -lrseq -o /linux/output/rseq/basic_test
  /usr/bin/ld: cannot find -lrseq
  collect2: error: ld returned 1 exit status

This is because the library search path points to the source
directory, not the output.

We can fix it by changing the library search path to $(OUTPUT).
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/rseq/Makefile

@@ -4,7 +4,7 @@ ifneq ($(shell $(CC) --version 2>&1 | head -n 1 | grep clang),)
 CLANG_FLAGS += -no-integrated-as
 endif
 
-CFLAGS += -O2 -Wall -g -I./ -I../../../../usr/include/ -L./ -Wl,-rpath=./ \
+CFLAGS += -O2 -Wall -g -I./ -I../../../../usr/include/ -L$(OUTPUT) -Wl,-rpath=./ \
 	  $(CLANG_FLAGS)
 LDLIBS += -lpthread