[easylog]if statement can be constexpr (#494)

Author: scuzqy

include/ylt/easylog.hpp

@@ -213,7 +213,7 @@ inline void add_appender(std::function<void(std::string_view)> fn) {
         easylog::record_t(std::chrono::system_clock::now(), severity, \
                           GET_STRING(__FILE__, __LINE__))             \
             .sprintf(fmt, __VA_ARGS__);                               \
-    if (severity == easylog::Severity::CRITICAL) {                    \
+    if constexpr (severity == easylog::Severity::CRITICAL) {          \
       easylog::flush<Id>();                                           \
       std::exit(EXIT_FAILURE);                                        \
     }                                                                 \
@@ -240,7 +240,7 @@ inline void add_appender(std::function<void(std::string_view)> fn) {
         easylog::record_t(std::chrono::system_clock::now(), severity, \
                           GET_STRING(__FILE__, __LINE__))             \
             .format(prefix::format(format_str, __VA_ARGS__));         \
-    if (severity == easylog::Severity::CRITICAL) {                    \
+    if constexpr (severity == easylog::Severity::CRITICAL) {          \
       easylog::flush<Id>();                                           \
       std::exit(EXIT_FAILURE);                                        \
     }                                                                 \