configure: Invert --enable-asm help string since default is now enabled

configure.ac

@@ -183,8 +183,8 @@ AC_ARG_ENABLE([glibc-back-compat],
   [use_glibc_compat=no])
 
 AC_ARG_ENABLE([asm],
-  [AS_HELP_STRING([--enable-asm],
+  [AS_HELP_STRING([--disable-asm],
-  [Enable assembly routines (default is yes)])],
+  [disable assembly routines (enabled by default)])],
   [use_asm=$enableval],
   [use_asm=yes])