Don't build empty cpp files

We shouldn't be compiling these .cpp files at all on other platforms,
rather than compiling empty .cpp files (which later results in "... has
no symbols" warnings).

llarp/CMakeLists.txt

@@ -7,7 +7,6 @@ add_library(lokinet-util
   util/buffer.cpp
   util/fs.cpp
   util/json.cpp
-  util/logging/android_logger.cpp
   util/logging/buffer.cpp
   util/logging/file_logger.cpp
   util/logging/logger.cpp
@@ -15,7 +14,6 @@ add_library(lokinet-util
   util/logging/loglevel.cpp
   util/logging/ostream_logger.cpp
   util/logging/syslog_logger.cpp
-  util/logging/win32_logger.cpp
   util/lokinet_init.c
   util/mem.cpp
   util/printer.cpp
@@ -38,7 +36,10 @@ target_link_libraries(lokinet-util PUBLIC
 )
 
 if(ANDROID)
+  target_sources(lokinet-util PRIVATE util/logging/android_logger.cpp)
   target_link_libraries(lokinet-util PUBLIC log)
+elseif(WIN32)
+  target_sources(lokinet-util PRIVATE util/logging/win32_logger.cpp)
 endif()
 
 add_library(lokinet-platform

llarp/util/logging/android_logger.cpp

@@ -1,5 +1,3 @@
-#if defined(ANDROID)
-
 #include "android_logger.hpp"
 #include "logger_internal.hpp"
 
@@ -69,4 +67,3 @@ namespace llarp
 
   }  // namespace llarp
 }  // namespace llarp
-#endif

llarp/util/logging/win32_logger.cpp

@@ -1,4 +1,3 @@
-#if defined(_WIN32)
 #include "win32_logger.hpp"
 #include "logger_internal.hpp"
 
@@ -113,4 +112,3 @@ namespace llarp
   }
 
 }  // namespace llarp
-#endif