maint: correct quoting for gl_WARN_ADD

3 out of 4 uses of gl_WARN_ADD() were incorrectly adding "" around
the argument, which in turn resulted in the argument being used
unquoted (configure had gl_positive=""-fstack-protector-all"",
rather than the intended gl_positive="-fstack-protector-all").
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NAndrea Bolognani <abologna@redhat.com>

m4/virt-compile-warnings.m4

@@ -194,8 +194,8 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
     # This should be < 256 really. Currently we're down to 4096,
     # but using 1024 bytes sized buffers (mostly for virStrerror)
     # stops us from going down further
-    gl_WARN_ADD(["-Wframe-larger-than=4096"], [STRICT_FRAME_LIMIT_CFLAGS])
-    gl_WARN_ADD(["-Wframe-larger-than=25600"], [RELAXED_FRAME_LIMIT_CFLAGS])
+    gl_WARN_ADD([-Wframe-larger-than=4096], [STRICT_FRAME_LIMIT_CFLAGS])
+    gl_WARN_ADD([-Wframe-larger-than=25600], [RELAXED_FRAME_LIMIT_CFLAGS])
 
     # Extra special flags
     dnl -fstack-protector stuff passes gl_WARN_ADD with gcc
@@ -250,7 +250,7 @@ AC_DEFUN([LIBVIRT_COMPILE_WARNINGS],[
         *-fstack-protector-strong*)
         ;;
         *)
-            gl_WARN_ADD(["-fstack-protector-all"])
+            gl_WARN_ADD([-fstack-protector-all])
         ;;
         esac
         ;;