include each header only once

Author: dschuff

test/test_other.py

@@ -9364,13 +9364,11 @@ def test_standalone_system_headers(self):
         inc = f'#include <{header}>\n__attribute__((weak)) int foo;\n'
         if cxx_only:
           create_file('a.cxx', inc)
-          create_file('b.cxx', inc)
-          self.run_process([EMXX, '-Werror', '-Wall', '-pedantic', 'a.cxx', 'b.cxx', '-E'], stdout=subprocess.DEVNULL)
+          self.run_process([EMXX, '-Werror', '-Wall', '-pedantic', 'a.cxx', '-E', '-o', 'a.i'])
         else:
           create_file('a.c', inc)
-          create_file('b.c', inc)
           for std in ([], ['-std=c89']):
-            self.run_process([EMCC] + std + ['-Werror', '-Wall', '-pedantic', 'a.c', 'b.c', '-E'], stdout=subprocess.DEVNULL)
+            self.run_process([EMCC] + std + ['-Werror', '-Wall', '-pedantic', 'a.c', '-E', '-o', 'a.i'])
 
   @is_slow_test
   @parameterized({