[PATCH BlueZ] build: use abspath for lib/bluetooth

When building from out of tree, and the top build dir was specified as
an absolute path, the linked headers in ${builddir}/lib/bluetooth were
broken.  This patch fixes it by relying on make's abspath macro as
opposed to the path concatenation.
---
 Makefile.am | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile.am b/Makefile.am
index eaed632e8..ad638cbb2 100644
--- a/Makefile.am
+++ b/Makefile.am

@@ -499,7 +499,7 @@ $(lib_libbluetooth_la_OBJECTS): $(local_headers)
 
 lib/bluetooth/%.h: lib/%.h
 	$(AM_V_at)$(MKDIR_P) lib/bluetooth
-	$(AM_V_GEN)$(LN_S) -f "$(abs_top_builddir)"/$< $@
+	$(AM_V_GEN)$(LN_S) -f $(abspath $<) $@
 
 if COVERAGE
 clean-coverage:

-- 
2.14.1.342.g6490525c54-goog