build: expand ASAN acronym in configure help

There is lots of space to expand this not-so-well-known acronym in the
option usage message.

PR-URL: #32325
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

configure.py

@@ -574,7 +574,7 @@
 parser.add_option('--enable-asan',
     action='store_true',
     dest='enable_asan',
-    help='build with asan')
+    help='compile for Address Sanitizer to find memory bugs')
 
 parser.add_option('--enable-static',
     action='store_true',