Add some comments to emscripten_time.c. NFC (emscripten-core#26285)

As an internal detail we also skip defining the `__` prefixed versions,
since they are not used anywhere and not part of the musl impl either.

Landing this instead of emscripten-core#26284

Author: sbc100

system/lib/libc/emscripten_time.c

@@ -5,33 +5,32 @@
  * found in the LICENSE file.
  */
 
-#include <emscripten/html5.h> // For `emscripten_data_now`
+#include <emscripten/html5.h> // For `emscripten_date_now`
 #include <time.h>
 #include <sys/time.h>
 
-#include "libc.h" // For `weak`/`weak_alias`
+#include "libc.h" // For `weak`
 
-
-time_t __time(time_t *t) {
+// emscripten-specific implementations. These works out slightly smaller than
+// musl's since it they avoid depending on the more general clock_gettime.
+weak time_t time(time_t *t) {
   double ret = emscripten_date_now() / 1000;
   if (t) {
     *t = ret;
   }
   return ret;
 }
 
-int __gettimeofday(struct timeval *restrict tv, void *restrict tz) {
+weak int gettimeofday(struct timeval *restrict tv, void *restrict tz) {
   double now_ms = emscripten_date_now();
   long long now_s = now_ms / 1000;
   tv->tv_sec = now_s; // seconds
   tv->tv_usec = (now_ms - (now_s * 1000)) * 1000; // microseconds
   return 0;
 }
 
+// Non-standard glibc/BSD extension that is not implemented by musl
 weak int dysize(int year) {
   int leap = ((year % 4 == 0) && ((year % 100 != 0) || (year % 400 == 0)));
   return leap ? 366 : 365;
 }
-
-weak_alias(__time, time);
-weak_alias(__gettimeofday, gettimeofday);

test/codesize/test_codesize_hello_dylink_all.json

@@ -1,7 +1,7 @@
 {
   "a.out.js": 244691,
-  "a.out.nodebug.wasm": 577706,
-  "total": 822397,
+  "a.out.nodebug.wasm": 577678,
+  "total": 822369,
   "sent": [
     "IMG_Init",
     "IMG_Load",
@@ -1708,7 +1708,6 @@
     "__getf2",
     "__getitimer",
     "__gettextdomain",
-    "__gettimeofday",
     "__gnu_f2h_ieee",
     "__gnu_h2f_ieee",
     "__gtdf2",
@@ -1909,7 +1908,6 @@
     "__syscall_wait4",
     "__sysv_signal",
     "__threwValue",
-    "__time",
     "__timezone",
     "__tolower_l",
     "__toupper_l",
@@ -3575,7 +3573,6 @@
     "$__getopt_long_core",
     "$__getopt_msg",
     "$__gettextdomain",
-    "$__gettimeofday",
     "$__gmtime_r",
     "$__gnu_f2h_ieee",
     "$__gnu_h2f_ieee",
@@ -3770,7 +3767,6 @@
     "$__tan",
     "$__tandf",
     "$__tanl",
-    "$__time",
     "$__tolower_l",
     "$__toread",
     "$__toupper_l",
@@ -4323,6 +4319,7 @@
     "$getsubopt",
     "$gettext",
     "$gettid",
+    "$gettimeofday",
     "$getw",
     "$getwc",
     "$getwchar",
@@ -4884,6 +4881,7 @@
     "$thrd_exit",
     "$thrd_join",
     "$thrd_sleep",
+    "$time",
     "$timegm",
     "$times",
     "$timespec_get",