C++: Fix non-private imports.

Author: jcreedcmu

cpp/ql/src/semmle/code/cpp/rangeanalysis/NanAnalysis.qll

@@ -1,5 +1,5 @@
 import cpp
-import semmle.code.cpp.rangeanalysis.RangeSSA
+private import semmle.code.cpp.rangeanalysis.RangeSSA
 
 /**
  * Holds if `guard` won't return the value `polarity` when either

cpp/ql/src/semmle/code/cpp/rangeanalysis/SimpleRangeAnalysis.qll

@@ -45,7 +45,7 @@ import cpp
 private import RangeAnalysisUtils
 import RangeSSA
 import SimpleRangeAnalysisCached
-import NanAnalysis
+private import NanAnalysis
 
 /**
  * This fixed set of lower bounds is used when the lower bounds of an