[cling] Provide C value printer, adopted from Ruben De Smet!

Fixes root-project/cling#364
Fixes root-project/cling#419

Adapts the corresponding ctest

Author: ferdymercury

interpreter/cling/lib/Interpreter/ValueExtractionSynthesizer.cpp

@@ -22,6 +22,14 @@
 #include "clang/Sema/Sema.h"
 #include "clang/Sema/SemaDiagnostic.h"
 
+// Implements the CValueExtractionPrinter interface.
+extern "C" {
+CLING_LIB_EXPORT
+void cling_SetValueNoAlloc(void* /*cling::Value* V*/) {}
+CLING_LIB_EXPORT
+void cling_SetValueWithAlloc(void* /*cling::Value* V*/) {}
+}
+
 using namespace clang;
 
 namespace cling {
@@ -436,6 +444,10 @@ namespace {
         return VSError(m_Sema, E, "cling::runtime::gCling");
       if (!(NSD = utils::Lookup::Namespace(m_Sema, "internal", NSD)))
         return VSError(m_Sema, E, "cling::runtime::internal namespace");
+    } else {
+      // C, ObjC,...
+      if (!(NSD = utils::Lookup::Namespace(m_Sema, "cling")))
+        return VSError(m_Sema, E, "cling namespace");
     }
     LookupResult R(*m_Sema, &m_Context->Idents.get("setValueNoAlloc"),
                    SourceLocation(), Sema::LookupOrdinaryName,

interpreter/cling/test/Driver/C.c

@@ -11,13 +11,13 @@
 
 // Validate cling C mode.
 
-// Fix value printing!
-
 int printf(const char*,...);
 printf("CHECK 123 %p\n", gCling); // CHECK: CHECK 123
 
-12 // expected-error {{ValueExtractionSynthesizer could not find: 'cling::runtime::internal::setValueNoAlloc'.}}
-
-32 // expected-error {{ValueExtractionSynthesizer could not find: 'cling::runtime::internal::setValueNoAlloc'.}}
+int i = 1 // CHECK: (int) 1
+sizeof(int) // CHECK: (unsigned long) 4
+int x = sizeof(int);
+printf("CHECK %d\n", x); // CHECK: CHECK 4
 
+// expected-no-diagnostics
 .q