Port to IBM xlc 12.01

Work around a compiler bug by using a separate enum for alignment.
* src/alloc.c (roundup_size): Declare in a separate enum.

src/alloc.c

@@ -2922,19 +2922,16 @@ set_next_vector (struct Lisp_Vector *v, struct Lisp_Vector *p)
 
 #define VECTOR_BLOCK_SIZE 4096
 
-enum
-  {
-    /* Alignment of struct Lisp_Vector objects.  Because pseudovectors
+/* Alignment of struct Lisp_Vector objects.  Because pseudovectors
    can contain any C type, align at least as strictly as
    max_align_t.  On x86 and x86-64 this can waste up to 8 bytes
    for typical vectors, since alignof (max_align_t) is 16 but
    typical vectors need only an alignment of 8.  However, it is
    not worth the hassle to avoid wasting those bytes.  */
-    vector_alignment = COMMON_MULTIPLE (alignof (max_align_t), GCALIGNMENT),
+enum {vector_alignment = COMMON_MULTIPLE (alignof (max_align_t), GCALIGNMENT)};
 
-    /* Vector size requests are a multiple of this.  */
-    roundup_size = COMMON_MULTIPLE (vector_alignment, word_size)
-  };
+/* Vector size requests are a multiple of this.  */
+enum { roundup_size = COMMON_MULTIPLE (vector_alignment, word_size) };
 
 /* Verify assumptions described above.  */
 verify (VECTOR_BLOCK_SIZE % roundup_size == 0);