Remove unnecessary dependency on stderr debug builds. NFC

In debug builds this stub version was bringing in other dependencies via
`getpid` -> `__syscall_getpid` -> `stderr`.  Due to the way object file
dependecies get resolved this means that any dependency on any function
in `library_pthread_stub.c` was bringing in `stderr` which in turn adds
`__stdio_write/read/lseek` to the wasm table (which is not amenable to
DCE).

This change solves the issue in two separate ways:

1. Move move_emscripten_main_browser_thread_id in pthread_self_stub.c
   meaning the dependency on getpid() is more specific.
2. Avoid the use of `stderr` in `emscripten_syscall_stubs.c`

Author: sbc100

system/lib/libc/emscripten_syscall_stubs.c

@@ -21,6 +21,7 @@
 #include <sys/stat.h>
 #include <time.h>
 #include <sys/utsname.h>
+#include <emscripten/console.h>
 
 static int g_pid = 42;
 static int g_pgid = 42;
@@ -32,7 +33,7 @@ static mode_t g_umask = S_IRWXU | S_IRWXG | S_IRWXO;
 #define REPORT(name)
 #else
 #define REPORT(name) \
-  fprintf(stderr, "warning: unsupported syscall: __syscall_" #name "\n");
+  emscripten_console_error("warning: unsupported syscall: __syscall_" #name "\n");
 #endif
 
 #define UNIMPLEMENTED(name, args) \

system/lib/pthread/library_pthread_stub.c

@@ -220,10 +220,6 @@ weak_alias(__pthread_detach, emscripten_builtin_pthread_detach);
 weak_alias(__pthread_detach, pthread_detach);
 weak_alias(__pthread_detach, thrd_detach);
 
-pthread_t emscripten_main_browser_thread_id() {
-  return __pthread_self();
-}
-
 // pthread_equal is defined as a macro in C, as a function for C++; undef it
 // here so we define the function for C++ that links to us.
 #ifdef pthread_equal

system/lib/pthread/pthread_self_stub.c

@@ -20,6 +20,10 @@ static long dummy_getpid() {
 }
 weak_alias(dummy_getpid, __syscall_getpid);
 
+pthread_t emscripten_main_browser_thread_id() {
+  return &__main_pthread;
+}
+
 __attribute__((constructor))
 static void init_pthread_self(void) {
   __main_pthread.locale = &libc.global_locale;

tests/other/metadce/hello_world.funcs

@@ -7,14 +7,11 @@ $__fwritex
 $__get_tp
 $__lock
 $__lockfile
-$__lseek
 $__lshrti3
 $__memcpy
 $__ofl_lock
 $__ofl_unlock
 $__original_main
-$__stdio_close
-$__stdio_seek
 $__stdio_write
 $__syscall_getpid
 $__towrite
@@ -24,7 +21,6 @@ $__unlockfile
 $__vfprintf_internal
 $__wasi_syscall_ret
 $__wasm_call_ctors
-$dummy
 $dynCall_jiji
 $emscripten_stack_get_end
 $emscripten_stack_get_free
@@ -39,7 +35,6 @@ $getint
 $getpid
 $init_pthread_self
 $isdigit
-$legalfunc$__wasi_fd_seek
 $legalstub$dynCall_jiji
 $main
 $memchr

tests/other/metadce/hello_world.imports

@@ -1,5 +1,3 @@
 env.emscripten_memcpy_big
 env.setTempRet0
-wasi_snapshot_preview1.fd_close
-wasi_snapshot_preview1.fd_seek
 wasi_snapshot_preview1.fd_write

tests/other/metadce/hello_world.jssize

@@ -1 +1 @@
-125729
+125367

tests/other/metadce/hello_world.sent

@@ -1,5 +1,3 @@
 emscripten_memcpy_big
-fd_close
-fd_seek
 fd_write
 setTempRet0

tests/other/metadce/hello_world.size

@@ -1 +1 @@
-12408
+12066