Makefile.am: Ship Meson assembly test files in the tarball

These were forgotten in commit 0ea37df4286e (meson: store ARM SIMD and
NEON tests as text files) and since autotools doesn't use them make
distcheck still succeeded.

Fixes #30

Signed-off-by: Matt Turner <mattst88@gmail.com>
diff --git a/Makefile.am b/Makefile.am
index 212d0a1..e33b2b9 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -26,6 +26,8 @@
 	Makefile.win32.common		\
 	meson.build			\
 	meson_options.txt		\
+	neon-test.S			\
+	arm-simd-test.S			\
 	$(NULL)
 
 tar_gz = $(PACKAGE)-$(VERSION).tar.gz