build: fix out of tree builds

The test directory needs -I$(top_srcdir) in order to find the
header files provided by the project itself.  When doing an in-tree
build, this is done automatically by automake due to 'config.h'
being generated in the root.

Change-Id: I3ea13eda98a73122f370a70ecf1f8d2c66540346
Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
diff --git a/test/Makefile.am b/test/Makefile.am
index f7c41bd..15e8f72 100644
--- a/test/Makefile.am
+++ b/test/Makefile.am
@@ -1,3 +1,4 @@
+AM_CPPFLAGS = -I$(top_srcdir)
 check_PROGRAMS =
 
 TESTS = $(check_PROGRAMS)