do not use fstack-protector unconditionally

package/davfs2/patches/patch-src_Makefile_am

@@ -0,0 +1,12 @@
+--- davfs2-1.5.2.orig/src/Makefile.am	2014-04-22 21:19:02.000000000 +0200
++++ davfs2-1.5.2/src/Makefile.am	2015-10-20 07:52:29.000000000 +0200
+@@ -32,8 +32,7 @@ mount_davfs_SOURCES = cache.c dav_coda.c
+         kernel_interface.h mount_davfs.h webdav.h
+ umount_davfs_SOURCES = umount_davfs.c defaults.h
+ 
+-AM_CFLAGS = -Wall -Werror=format-security \
+-        -fstack-protector --param=ssp-buffer-size=4
++AM_CFLAGS = -Wall -Werror=format-security
+ DEFS = -DPROGRAM_NAME=\"mount.davfs\" \
+        -DDAV_SYS_CONF_DIR=\"$(pkgsysconfdir)\" \
+        -DDAV_LOCALSTATE_DIR=\"$(dav_localstatedir)\" \