Correctly compute the type of an assignment expression.

This change enables following types of statements to work correctly:

    a = b = 3;
    if ((a = getchar()) < 0) { ... }

This fixes 2232082 acc: assignment in comparison segfaults

libacc/acc.cpp

@@ -1666,6 +1666,7 @@ class Compiler : public ErrorSink {
                             pDestType->tag);
                     break;
             }
+            setR0Type(pDestType);
         }
 
         virtual void loadR0FromR0() {
@@ -2836,6 +2837,7 @@ class Compiler : public ErrorSink {
                             pTargetType->tag);
                     break;
             }
+            setR0Type(pTargetType);
         }
 
         virtual void loadR0FromR0() {

libacc/tests/data/assignment.c

@@ -0,0 +1,9 @@
+int main() {
+    int a = 0;
+    int b = 1;
+    a = b = 2; // Test that "b = 2" generates an rvalue.
+    if (a = 7) { // Test that a = 7 generates an rvalue.
+        b = 3;
+    }
+    return a;
+}

libacc/tests/test.py

@@ -424,6 +424,11 @@ result: 0
     def testShort(self):
         self.compileCheck(["-R", "data/short.c"], """Executing compiled code:
 result: -2
+""","""""")
+
+    def testAssignment(self):
+        self.compileCheck(["-R", "data/assignment.c"], """Executing compiled code:
+result: 7
 ""","""""")
 
     def testArray(self):