Fixes UBSAN errors such as:

../src/spvw_typealloc.d:146:450: runtime error: member access within misaligned address 0x17000000009c for type 'struct s8string_', which requires 8 byte alignment
0x17000000009c: note: pointer points here
  53 45 52 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00
              ^ 

--- src/lispbibl.d.orig	2025-02-07 19:25:44.207789666 -0700
+++ src/lispbibl.d	2025-02-10 11:38:31.029348227 -0700
@@ -6006,7 +6006,7 @@ typedef signed_int_with_n_bits(intVsize)
 #if defined(I80386) || defined(POWERPC) || defined(ARM) || defined(S390)
   #define varobject_alignment  4
 #endif
-#if defined(SPARC) || defined(HPPA) || defined(MIPS) || defined(DECALPHA) || defined(IA64) || defined(AMD64) || defined(ARM64) || defined(RISCV64) || defined(LOONGARCH64)
+#if defined(SPARC) || defined(HPPA) || defined(MIPS) || defined(DECALPHA) || defined(IA64) || defined(AMD64) || defined(ARM64) || defined(RISCV64) || defined(LOONGARCH64) || defined(POWERPC64)
   #define varobject_alignment  8
 #endif
 #if (!defined(TYPECODES) || defined(GENERATIONAL_GC)) && (varobject_alignment < 4)