Improve test_multiply_defined_libsymbols (#26953)

This test was first added in c735bb6. Hopefully these changes make it
more obvious what is being tested, and also test more commonly used
flags (`-shared` vs `-r`).

Split out from #25930.

Author: sbc100

test/common.py

@@ -1232,7 +1232,7 @@ def emcc(self, filename, args=[], **kwargs):  # noqa
     filename = maybe_test_file(filename)
     compile_only = '-c' in args or '-sSIDE_MODULE' in args
     cmd = [compiler_for(filename), filename] + self.get_cflags(compile_only=compile_only) + args
-    self.run_process(cmd, **kwargs)
+    return self.run_process(cmd, **kwargs)
 
   # Shared test code between main suite and others
 

test/test_other.py

@@ -1353,13 +1353,19 @@ def test_multiply_defined_libsymbols(self):
       }
     ''')
 
+    # Check linking libA.so multiple times (both directly and indirectly) does not result
+    # any multiply defined symbols.  This is especially important with `FAKE_DYLIBS` where
+    # we model shared libraries using regular object files.  Without special handling
+    # fake `libA.so` could get linked multiple times.
     self.cflags.remove('-Werror')
     self.emcc('libA.c', ['-shared', '-o', 'libA.so'])
 
-    self.emcc('a2.c', ['-r', '-L.', '-lA', '-o', 'a2.o'])
-    self.emcc('b2.c', ['-r', '-L.', '-lA', '-o', 'b2.o'])
+    err = self.emcc('a2.c', ['-shared', '-L.', '-lA', '-o', 'liba2.so'], stderr=PIPE).stderr
+    self.assertContained('emcc: warning: ignoring dynamic library libA.so when generating an object file', err)
+    err = self.emcc('b2.c', ['-shared', '-L.', '-lA', '-o', 'libb2.so'], stderr=PIPE).stderr
+    self.assertContained('emcc: warning: ignoring dynamic library libA.so when generating an object file', err)
 
-    self.do_runf('main.c', 'result: 1', cflags=['-L.', '-lA', 'a2.o', 'b2.o'])
+    self.do_runf('main.c', 'result: 1', cflags=['-L.', '-lA', 'liba2.so', 'libb2.so'])
 
   def test_multiply_defined_libsymbols_2(self):
     create_file('a.c', "int x() { return 55; }")