[Docs] Mention that ASSERTIONS are disabled in -O1+ (#23823)

Author: kripken

site/source/docs/tools_reference/settings_reference.rst

@@ -23,6 +23,7 @@ Whether we should add runtime assertions. This affects both JS and how
 system libraries are built.
 ASSERTIONS == 2 gives even more runtime checks, that may be very slow. That
 includes internal dlmalloc assertions, for example.
+ASSERTIONS defaults to 0 in optimized builds (-O1 and above).
 
 Default value: 1
 

src/settings.js

@@ -47,6 +47,7 @@
 // system libraries are built.
 // ASSERTIONS == 2 gives even more runtime checks, that may be very slow. That
 // includes internal dlmalloc assertions, for example.
+// ASSERTIONS defaults to 0 in optimized builds (-O1 and above).
 // [link]
 var ASSERTIONS = 1;