[analyzer] Replace bug category magic strings with shared constants, take 2.

Re-commit r191910 (reverted in r191936) with layering violation fixed, by
moving the bug categories to StaticAnalyzerCore instead of ...Checkers.

llvm-svn: 191937
diff --git a/clang/lib/StaticAnalyzer/Checkers/CheckSizeofPointer.cpp b/clang/lib/StaticAnalyzer/Checkers/CheckSizeofPointer.cpp
index f2c5050..3eeb948 100644
--- a/clang/lib/StaticAnalyzer/Checkers/CheckSizeofPointer.cpp
+++ b/clang/lib/StaticAnalyzer/Checkers/CheckSizeofPointer.cpp
@@ -65,7 +65,7 @@
       PathDiagnosticLocation::createBegin(E, BR.getSourceManager(), AC);
     BR.EmitBasicReport(AC->getDecl(),
                        "Potential unintended use of sizeof() on pointer type",
-                       "Logic",
+                       categories::LogicError,
                        "The code calls sizeof() on a pointer type. "
                        "This can produce an unexpected result.",
                        ELoc, &R, 1);