[BOLT] Issue error in relocs mode if input is lacking relocations.

Summary:
If we specify "-relocs" flag and an input has no relocations we
proceed with assumptions that relocations were there and break the
binary.

Detect the condition above, and reject the input.

(cherry picked from FBD4761239)

bolt/RewriteInstance.cpp

@@ -1250,6 +1250,8 @@ BinaryFunction *RewriteInstance::createBinaryFunction(
 }
 
 void RewriteInstance::readSpecialSections() {
+  bool HasTextRelocations = false;
+
   // Process special sections.
   for (const auto &Section : InputFile->sections()) {
     StringRef SectionName;
@@ -1268,6 +1270,8 @@ void RewriteInstance::readSpecialSections() {
       DebugLocSize = Section.getSize();
     } else if (SectionName == ".eh_frame") {
       EHFrameSection = Section;
+    } else if (SectionName == ".rela.text") {
+      HasTextRelocations = true;
     }
 
     // Ignore zero-size allocatable sections as they present no interest to us.
@@ -1278,6 +1282,12 @@ void RewriteInstance::readSpecialSections() {
     }
   }
 
+  if (opts::Relocs && !HasTextRelocations) {
+    errs() << "BOLT-ERROR: relocations against code are missing from the input "
+              "file. Cannot proceed in relocations mode (-relocs).\n";
+    exit(1);
+  }
+
   // Process debug sections.
   EHFrame = BC->DwCtx->getEHFrame();
   if (opts::DumpEHFrame) {