[test] Pass filename explicitly to compile_btest helper. NFC

This allows us to use `compiler_for` to determine whether to run
`EMCC` or `EMXX` appropriately.

test/common.py

@@ -833,6 +833,11 @@ def setUp(self):
     self.js_engines = config.JS_ENGINES.copy()
     self.settings_mods = {}
     self.emcc_args = ['-Wclosure', '-Werror', '-Wno-limited-postlink-optimizations']
+    # TODO(https://github.com/emscripten-core/emscripten/issues/11121)
+    # For historical reasons emcc compiles and links as C++ by default.
+    # However we want to run our tests in a more strict manner.  We can
+    # remove this if the issue above is ever fixed.
+    self.set_setting('NO_DEFAULT_TO_CXX')
     self.ldflags = []
     # Increate stack trace limit to maximise usefulness of test failure reports
     self.node_args = ['--stack-trace-limit=50']
@@ -954,9 +959,13 @@ def has_changed_setting(self, key):
   def clear_setting(self, key):
     self.settings_mods.pop(key, None)
 
-  def serialize_settings(self):
+  def serialize_settings(self, ldflags=True):
     ret = []
+    # Incomplete list of link-only settings
+    link_only_settings = ['NO_DEFAULT_TO_CXX', 'DEFAULT_LIBRARY_FUNCS_TO_INCLUDE']
     for key, value in self.settings_mods.items():
+      if not ldflags and key in link_only_settings:
+        continue
       if value == 1:
         ret.append(f'-s{key}')
       elif type(value) is list:
@@ -994,7 +1003,7 @@ def get_emcc_args(self, main_file=False, ldflags=True):
     def is_ldflag(f):
       return any(f.startswith(s) for s in ['-sENVIRONMENT=', '--pre-js=', '--post-js='])
 
-    args = self.serialize_settings() + self.emcc_args
+    args = self.serialize_settings(ldflags) + self.emcc_args
     if ldflags:
       args += self.ldflags
     else:
@@ -2106,24 +2115,26 @@ def reftest(self, expected, manually_trigger=False):
       setupRefTest();
 ''' % (reporting, basename, int(manually_trigger)))
 
-  def compile_btest(self, args, reporting=Reporting.FULL):
+  def compile_btest(self, filename, args, reporting=Reporting.FULL):
     # Inject support code for reporting results. This adds an include a header so testcases can
     # use REPORT_RESULT, and also adds a cpp file to be compiled alongside the testcase, which
     # contains the implementation of REPORT_RESULT (we can't just include that implementation in
     # the header as there may be multiple files being compiled here).
     if reporting != Reporting.NONE:
       # For basic reporting we inject JS helper funtions to report result back to server.
-      args += ['-DEMTEST_PORT_NUMBER=%d' % self.port,
-               '--pre-js', test_file('browser_reporting.js')]
+      args += ['--pre-js', test_file('browser_reporting.js')]
       if reporting == Reporting.FULL:
         # If C reporting (i.e. REPORT_RESULT macro) is required
         # also compile in report_result.c and forice-include report_result.h
-        args += ['-I' + TEST_ROOT,
-                 '-include', test_file('report_result.h'),
-                 test_file('report_result.c')]
+        self.run_process([EMCC, '-c', '-I' + TEST_ROOT,
+                          '-DEMTEST_PORT_NUMBER=%d' % self.port,
+                          test_file('report_result.c')] + self.get_emcc_args(ldflags=False))
+        args += ['report_result.o', '-include', test_file('report_result.h')]
     if EMTEST_BROWSER == 'node':
       args.append('-DEMTEST_NODE')
-    self.run_process([EMCC] + self.get_emcc_args() + args)
+    if not os.path.exists(filename):
+      filename = test_file(filename)
+    self.run_process([compiler_for(filename), filename] + self.get_emcc_args() + args)
 
   def btest_exit(self, filename, assert_returncode=0, *args, **kwargs):
     """Special case of btest that reports its result solely via exiting
@@ -2166,10 +2177,10 @@ def btest(self, filename, expected=None, reference=None,
       # manual_reference only makes sense for reference tests
       assert manual_reference is None
     outfile = output_basename + '.html'
-    args += [filename, '-o', outfile]
+    args += ['-o', outfile]
     # print('all args:', args)
     utils.delete_file(outfile)
-    self.compile_btest(args, reporting=reporting)
+    self.compile_btest(filename, args, reporting=reporting)
     self.assertExists(outfile)
     if post_build:
       post_build()