[Linux]Add build arg to allow external logging implementation (#22829)

* Linux: add build arg to allow external logging implementation

The will allow target platform/application to provide its own
logging implementation, such as writing logs to file, instead
of logging to stdout.

* Update core.gni

src/lib/core/core.gni

@@ -47,6 +47,11 @@ declare_args() {
   # Configure chip logging to output through pigweed logging.
   chip_use_pw_logging = false
 
+  # Configure chip logging to output through external logging implementation.
+  # External code will need to provide implementation for CHIP log output
+  # function (LogV), which is defined in "src/platform/logging/LogV.h".
+  chip_use_external_logging = false
+
   # Enable short error strings.
   chip_config_short_error_str = false
 

src/platform/Linux/BUILD.gn

@@ -67,7 +67,6 @@ static_library("Linux") {
     "InetPlatformConfig.h",
     "KeyValueStoreManagerImpl.cpp",
     "KeyValueStoreManagerImpl.h",
-    "Logging.cpp",
     "NetworkCommissioningDriver.h",
     "NetworkCommissioningEthernetDriver.cpp",
     "PlatformManagerImpl.cpp",
@@ -78,6 +77,10 @@ static_library("Linux") {
     "SystemTimeSupport.cpp",
   ]
 
+  if (!chip_use_external_logging) {
+    sources += [ "Logging.cpp" ]
+  }
+
   if (chip_enable_openthread) {
     sources += [ "NetworkCommissioningThreadDriver.cpp" ]
   }