Adds CMake variable to configure compile time log levels. (#1733)

* Adds cmake variable PCAPPP_LOG_LEVEL to determine compile time log level through cmake.

* Added checks for log level input.

* Lint?

Author: Dimi1010

CMakeLists.txt

@@ -85,6 +85,31 @@ if(PCAPPP_USE_SANITIZER)
   endif()
 endif()
 
+# Build options (Compile time log level)
+set(
+  PCAPP_ALLOWED_LOG_LEVELS
+  ""
+  "0"
+  "1"
+  "2"
+  "3"
+)
+set(
+  PCAPPP_LOG_LEVEL
+  ""
+  CACHE STRING
+  "Compile time log level (0 - Off, 1 - Error, 2 - Info, 3 - Debug) Default(empty): Debug"
+)
+set_property(CACHE PCAPPP_LOG_LEVEL PROPERTY STRINGS ${PCAPP_ALLOWED_LOG_LEVELS})
+
+if(NOT PCAPPP_LOG_LEVEL IN_LIST PCAPP_ALLOWED_LOG_LEVELS)
+  message(FATAL_ERROR "PCAPPP_LOG_LEVEL must be one of ${PCAPP_ALLOWED_LOG_LEVELS}")
+endif()
+
+if(PCAPPP_LOG_LEVEL)
+  add_compile_definitions("PCPP_ACTIVE_LOG_LEVEL=${PCAPPP_LOG_LEVEL}")
+endif()
+
 # Build options (Turn on Examples and Tests if it's the main project)
 option(PCAPPP_BUILD_EXAMPLES "Build Examples" ${PCAPPP_MAIN_PROJECT})
 cmake_dependent_option(