InstrProf: Promote this assert to a report_fatal_error

If this assert does fire, the no-asserts behaviour is an infinite
loop. It's better to crash in this case so we get a crash report and
stop wasting the user's cpu cycles.

llvm-svn: 242591

clang/lib/CodeGen/CoverageMappingGen.cpp

@@ -413,8 +413,8 @@ struct CounterCoverageMappingBuilder
           SourceRegions.emplace_back(Region.getCounter(), NestedLoc, EndLoc);
 
           EndLoc = getPreciseTokenLocEnd(getIncludeOrExpansionLoc(EndLoc));
-          assert(!EndLoc.isInvalid() &&
-                 "File exit was not handled before popRegions");
+          if (EndLoc.isInvalid())
+            llvm::report_fatal_error("File exit not handled before popRegions");
         }
         Region.setEndLoc(EndLoc);