Preserve system library ordering even under EMCC_FORCE_STDLIBS=1

In particular `EMCC_FORCE_STDLIBS=1` would previously place libc before
libbulkmemory which don't work.  libbulkmemory always needs to come
first on the link line.

Fixes: emscripten-core#22161

test/test_other.py

@@ -5876,6 +5876,11 @@ def test_only_force_stdlibs_2(self):
       self.run_process([EMXX, 'src.cpp', '-sDISABLE_EXCEPTION_CATCHING=0'])
     self.assertContained('Caught exception: std::exception', self.run_js('a.out.js'))
 
+  @with_env_modify({'EMCC_FORCE_STDLIBS': '1'})
+  def test_force_stdlibs(self):
+    self.do_runf('hello_world.c')
+    self.do_runf('hello_world.c', emcc_args=['-sWASM_BIGINT'])
+
   @crossplatform
   @also_with_env_modify({'gb_locale': {'LC_ALL': 'en_GB'}, 'long_tz': {'TZ': 'Asia/Kathmandu'}})
   def test_strftime_zZ(self):

tools/system_libs.py

@@ -2292,12 +2292,14 @@ def add_library(libname):
   if settings.SIDE_MODULE:
     return libs_to_link
 
-  for forced in force_include:
-    if forced not in system_libs_map:
-      shared.exit_with_error('invalid forced library: %s', forced)
-    add_library(forced)
+  def add_forced_libs():
+    for forced in force_include:
+      if forced not in system_libs_map:
+        shared.exit_with_error('invalid forced library: %s', forced)
+      add_library(forced)
 
   if '-nodefaultlibs' in args:
+    add_forced_libs()
     return libs_to_link
 
   sanitize = settings.USE_LSAN or settings.USE_ASAN or settings.UBSAN_RUNTIME
@@ -2323,6 +2325,7 @@ def add_sanitizer_libs():
       add_library('libsanitizer_common_rt')
 
   if only_forced:
+    add_forced_libs()
     add_library('libcompiler_rt')
     add_sanitizer_libs()
     return libs_to_link
@@ -2390,6 +2393,10 @@ def add_sanitizer_libs():
     add_library('libwasmfs')
 
   add_sanitizer_libs()
+
+  # Add forced stdlibs at the end so that the order of system libraries is
+  # still preserved above, even when EMCC_FORCE_STDLIBS=1 is used.
+  add_forced_libs()
   return libs_to_link