Change global const handling to silently ignore redeclarations

test/mjsunit/global-const-var-conflicts.js

 // Copyright 2008 the V8 project authors. All rights reserved.
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 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
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 //       with the distribution.
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 //       from this software without specific prior written permission.
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 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
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 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Check that dynamically introducing conflicting consts/vars
-// leads to exceptions.
+// is silently ignored (and does not lead to exceptions).
 
 var caught = 0;
 
 eval("const a");
 try { eval("var a"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertTrue(typeof a == 'undefined');
 try { eval("var a = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertTrue(typeof a == 'undefined');
 
 eval("const b = 0");
 try { eval("var b"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertEquals(0, b);
 try { eval("var b = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertEquals(0, b);
 
 eval("var c");
 try { eval("const c"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertTrue(typeof c == 'undefined');
 try { eval("const c = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertTrue(typeof c == 'undefined');
 
 eval("var d = 0");
 try { eval("const d"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertEquals(0, d);
 try { eval("const d = 1"); } catch (e) { caught++; assertTrue(e instanceof TypeError); }
 assertEquals(0, d);
 
-assertEquals(8, caught);
+assertEquals(0, caught);