vim.spec: Set FORTIFY_SOURCE to 1 as Vim upstream expects

vim.spec

@@ -37,6 +37,12 @@
 %define withruby 1
 %endif
 
+# VIm upstream wants to build with FORTIFY_SOURCE=1,
+# because higher levels causes crashes of valid code constructs
+# and their reimplementation would cost unnecessary maintenance
+# https://github.com/vim/vim/pull/3507
+%define _fortify_level 1
+
 %define baseversion 9.0
 %define vimdir vim90
 
@@ -429,6 +435,8 @@ perl -pi -e "s/vimrc/virc/"  os_unix.h
   --disable-canberra \
   --disable-libsodium
 
+echo $CFLAGS
+
 %make_build
 cp vim minimal-vim
 make clean