build: reduce usage of constexpr

some compilers has lack of proper support for that

modules/core/src/utils/logtagconfigparser.cpp

@@ -145,7 +145,7 @@ void LogTagConfigParser::parseNameAndLevel(const std::string& s)
 
 void LogTagConfigParser::parseWildcard(const std::string& name, LogLevel level)
 {
-    constexpr size_t npos = std::string::npos;
+    const size_t npos = std::string::npos;
     const size_t len = name.length();
     if (len == 0u)
     {

modules/core/src/utils/logtagmanager.cpp

@@ -10,6 +10,10 @@ namespace cv {
 namespace utils {
 namespace logging {
 
+
+const char* LogTagManager::m_globalName = "global";
+
+
 LogTagManager::LogTagManager(LogLevel defaultUnconfiguredGlobalLevel)
     : m_mutex()
     , m_globalLogTag(new LogTag(m_globalName, defaultUnconfiguredGlobalLevel))

modules/core/src/utils/logtagmanager.hpp

@@ -270,7 +270,7 @@ private:
     static bool internal_isNamePartMatch(MatchingScope scope, size_t matchingPos);
 
 private:
-    static constexpr const char* m_globalName = "global";
+    static const char* m_globalName;
 
 private:
     mutable MutexType m_mutex;