gcc-4.7 regression in 1bdaf9c8

[dabroz]

1bdaf9c introduced a problem that prevents gcc-4.7 (and other setups) from compiling mruby.

"gcc-4.7" -m32 -DMRB_INT64=1 -g3 -O0 -DMRB_DEBUG -DMRBGEM_MRUBY_ARRAY_EXT_VERSION=0.0.0 -I"/builds/dabroz/mruby/include" -MMD -o "/builds/dabroz/mruby/build/host/mrbgems/mruby-array-ext/src/array.o" -c "/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c"
/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c: In function 'mrb_ary_slice_bang':
/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c:213:3: error: 'for' loop initial declarations are only allowed in C99 mode
/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c:213:3: note: use option -std=c99 or -std=gnu99 to compile your code
/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c:218:16: error: redefinition of 'j'
/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c:213:16: note: previous definition of 'j' was here
/builds/dabroz/mruby/mrbgems/mruby-array-ext/src/array.c:218:3: error: 'for' loop initial declarations are only allowed in C99 mode

Problematic lines:

213  for (mrb_int j = i, k = 0; k < len; ++j, ++k) {
214    mrb_ary_push(mrb, ary, a->ptr[j]);
215  }
216
217  ptr = a->ptr + i;
218  for (mrb_int j = i; j <= a->len - len; ++j) {
219    *ptr = *(ptr+len);
220    ++ptr;
221  }