[C11] Add test & update status of N1282 and DR087

Our existing diagnostics for catching unsequenced modifications handles
test coverage for N1282, which is correcting the standard based on the
resolution of DR087.

Author: AaronBallman

clang/test/C/C11/n1282.c

@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -verify -Wunsequenced -Wno-unused-value %s
+
+/* WG14 N1282: Yes
+ * Clarification of Expressions
+ */
+
+int g;
+
+int f(int i) {
+  g = i;
+  return 0;
+}
+
+int main(void) {
+  int x;
+  x = (10, g = 1, 20) + (30, g = 2, 40); /* Line A */ // expected-warning {{multiple unsequenced modifications to 'g'}}
+  x = (10, f(1), 20) + (30, f(2), 40); /* Line B */
+  x = (g = 1) + (g = 2); /* Line C */                 // expected-warning {{multiple unsequenced modifications to 'g'}}
+  return 0;
+}

clang/test/C/drs/dr0xx.c

@@ -73,6 +73,10 @@
  * WG14 DR085: yes
  * Returning from main
  *
+ * WG14 DR087: yes
+ * Order of evaluation
+ * Note: this DR is covered by C/C11/n1282.c
+ *
  * WG14 DR086: yes
  * Object-like macros in system headers
  *

clang/www/c_dr_status.html

@@ -577,7 +577,7 @@ <h2 id="cdr">C defect report implementation status</h2>
     <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_087.html">87</a></td>
     <td>NAD</td>
     <td>Order of evaluation</td>
-    <td class="unknown" align="center">Unknown</td>
+    <td class="full" align="center">Yes</td>
   </tr>
   <tr id="88">
     <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/dr_088.html">88</a></td>

clang/www/c_status.html

@@ -401,7 +401,7 @@ <h2 id="c11">C11 implementation status</h2>
     <tr>
       <td>Clarification of expressions</td>
       <td><a href="https://www.open-std.org/jtc1/sc22/wg14/www/docs/n1282.pdf">N1282</a></td>
-      <td class="unknown" align="center">Unknown</td>
+      <td class="full" align="center">Yes</td>
     </tr>
     <tr>
       <td>Extending the lifetime of temporary objects (factored approach)</td>