glsl: Call check_builtin_array_max_size when redeclaring gl_in.

Normally when a built-in array (such as gl_ClipDistance) is
redeclared, we call get_variable_being_redeclared() to do the
redeclaration, and it in turn calls check_builtin_array_max_size() to
make sure that the redeclared array size isn't too large.

However when a built-in array is redeclared as part of redeclaring
gl_in, we don't call get_variable_being_redeclared() (since the
individual built-ins aren't each represented by their own ir_variable
anymore).  So we need to add an explicit call to
check_builtin_array_max_size() to make sure the new array size isn't
too large.

Note: at the moment this is redundant with a test that's done at link
time, so there's no change to piglit results.  But the patch that
follows will prevent link errors from being reported if gl_PerVertex
isn't used, so in order to prevent that patch from causing
regressions, we need to add the compile check now.  Besides, it's
nicer to report this error at compile time anyhow.