fixup! refactor: move string-utils, tr-assert, tr-macros to libtrbase.a

fix macOS build error

tr/base/CMakeLists.txt

@@ -28,7 +28,7 @@ target_sources(trbase
         serializer.h
         string-utils.cc
         string-utils.h
-        $<$<BOOL:${IS_APPLE_CLANG}>:string-utils.mm>
+        $<$<AND:$<BOOL:${APPLE}>,$<OR:$<CXX_COMPILER_ID:AppleClang>,$<CXX_COMPILER_ID:Clang>>>:string-utils.mm>
         tr-assert.cc
         tr-assert.h
         tr-getopt.cc

tr/torrent/CMakeLists.txt

@@ -10,11 +10,6 @@ add_compile_options(
 
 add_library(${TR_NAME} STATIC)
 
-set(IS_APPLE_CLANG FALSE)
-if(APPLE AND CMAKE_CXX_COMPILER_ID MATCHES "Clang")
-    set(IS_APPLE_CLANG TRUE)
-endif()
-
 target_sources(${TR_NAME}
     PRIVATE
         announce-list.cc