[clang-repl] Recover the lookup tables of the primary context.

Before this patch, there was re-declaration error if error was encountered in
the same line. The recovery support acted only if this type of error was
encountered in the first line of the program and not in subsequent lines.

For example:

```
clang-repl> int i=9;
clang-repl> int j=9; err;
input_line_3:1:5: error: redefinition of 'j'
int j = 9;
```

Differential revision: https://reviews.llvm.org/D123674

clang/lib/Interpreter/IncrementalParser.cpp

@@ -188,7 +188,7 @@ IncrementalParser::ParseOrWrapTopLevelDecl() {
     S.TUScope->setEntity(PreviousTU);
 
     // Clean up the lookup table
-    if (StoredDeclsMap *Map = PreviousTU->getLookupPtr()) {
+    if (StoredDeclsMap *Map = PreviousTU->getPrimaryContext()->getLookupPtr()) {
       for (auto I = Map->begin(); I != Map->end(); ++I) {
         StoredDeclsList &List = I->second;
         DeclContextLookupResult R = List.getLookupResult();

clang/test/Interpreter/execute.cpp

@@ -1,3 +1,4 @@
+// RUN: clang-repl "int x = 10;" "int y=7; err;" "int y = 10;"
 // RUN: clang-repl "int i = 10;" 'extern "C" int printf(const char*,...);' \
 // RUN:            'auto r1 = printf("i = %d\n", i);' | FileCheck --check-prefix=CHECK-DRIVER %s
 // REQUIRES: host-supports-jit