Fixed a few inconclusive warnings regarding const-correctness in cppcheck code base.

test/testmathlib.cpp

@@ -540,7 +540,7 @@ private:
         ASSERT_EQUALS(false, MathLib::isHex(""));
     }
 
-    void isValidSuffix(void) {
+    void isValidSuffix(void) const {
         // negative testing
         std::string value = "ux";
         ASSERT_EQUALS(false, MathLib::isValidSuffix(value.begin(), value.end()));

test/testtokenize.cpp

@@ -3167,7 +3167,7 @@ private:
         }
     }
 
-    void line2() {
+    void line2() const {
         const char code[] = "#line 8 \"c:\\a.h\"\n"
                             "123\n";