Missing comments from #15083. NFC. (#15092)

Not sure how I missed adding these.

Author: sbc100

src/library.js

@@ -2644,8 +2644,10 @@ LibraryManager.library = {
     {{{ makeEval('return eval(UTF8ToString(ptr))|0;') }}}
   },
 
-  emscripten_run_script_string__sig: 'ii',
+  // We use builtin_malloc and builtin_free here because otherwise lsan will
+  // report the last returned string as a leak.
   emscripten_run_script_string__deps: ['emscripten_builtin_malloc', 'emscripten_builtin_free'],
+  emscripten_run_script_string__sig: 'ii',
   emscripten_run_script_string: function(ptr) {
     {{{ makeEval("var s = eval(UTF8ToString(ptr));") }}}
     if (s == null) {
@@ -2930,6 +2932,8 @@ LibraryManager.library = {
     _emscripten_log_js(flags, str);
   },
 
+  // We never free the return values of this function so we need to allocate
+  // using builtin_malloc to avoid LSan reporting these as leaks.
   emscripten_get_compiler_setting__deps: ['emscripten_builtin_malloc'],
   emscripten_get_compiler_setting: function(name) {
 #if RETAIN_COMPILER_SETTINGS

system/lib/libc/musl/src/env/__environ.c

@@ -1,17 +1,19 @@
 #include "libc.h"
 
-#ifdef __EMSCRIPTEN__
-#include <stdlib.h>
-#include <wasi/api.h>
-#include <emscripten/emmalloc.h>
-#endif
-
 char **__environ = 0;
 weak_alias(__environ, ___environ);
 weak_alias(__environ, _environ);
 weak_alias(__environ, environ);
 
 #ifdef __EMSCRIPTEN__
+#include <stdlib.h>
+#include <wasi/api.h>
+// Included for emscripten_builtin_free / emscripten_builtin_malloc
+// TODO(sbc): Should these be in their own header to avoid emmalloc here?
+#include <emscripten/emmalloc.h>
+
+// We use emscripten_builtin_malloc here because this memory is never freed and
+// and we don't want LSan to consider this a leak.
 __attribute__((constructor(100))) // construct this before user code
 void __emscripten_environ_constructor(void) {
     size_t environ_count;

system/lib/pthread/emscripten_tls_init.c

@@ -5,6 +5,8 @@
  * found in the LICENSE file.
  */
 
+// Included for emscripten_builtin_free / emscripten_builtin_malloc
+// TODO(sbc): Should these be in their own header to avoid emmalloc here?
 #include <emscripten/emmalloc.h>
 #include <pthread.h>
 

system/lib/pthread/pthread_create.c

@@ -13,6 +13,8 @@
 #include <stdbool.h>
 #include <string.h>
 #include <threads.h>
+// Included for emscripten_builtin_free / emscripten_builtin_malloc
+// TODO(sbc): Should these be in their own header to avoid emmalloc here?
 #include <emscripten/emmalloc.h>
 
 // See musl's pthread_create.c