build regression in vm.c in 6.1.0

commit 56f71ea2 from pullrequest #14 (closed) causes a compile error:

[  123s] src/vm/vm.c: In function 'escaped_strcpy':
[  123s] src/vm/vm.c:178:5: error: 'for' loop initial declarations are only allowed in C99 mode
[  123s]      for(size_t i=0; i < len; i++ )
[  123s]      ^
[  123s] src/vm/vm.c:178:5: note: use option -std=c99 or -std=gnu99 to compile your code
[  123s] Makefile:609: recipe for target 'src/vm/vm.lo' failed

From remote, the added code looks like C++.