bug#61489: Increase BLOCK_ALIGN from 1024 to 32768

Originally discovered by Tyler Dodge in his article "Significant Garbage
Collection Improvement For Emacs".

While testing this change on Archlinux system with Intel i5-7200U CPU,
average time of garbage collection gets reduced by ≈25%. Other users
report improvements up to 50%. While monitoring PSS of emacs with and
without customizations loaded before and after the patch, no
statistically significant differences were discovered. So overall, this
change is a win.
* src/alloc.c (BLOCK_ALIGN): increase from 1024 to 32768.

Author: Hi-Angel

src/alloc.c

@@ -1083,7 +1083,7 @@ lisp_free (void *block)
    BLOCK_BYTES and guarantees they are aligned on a BLOCK_ALIGN boundary.  */
 
 /* Byte alignment of storage blocks.  */
-#define BLOCK_ALIGN (1 << 10)
+#define BLOCK_ALIGN (1 << 15)
 verify (POWER_OF_2 (BLOCK_ALIGN));
 
 /* Use aligned_alloc if it or a simple substitute is available.