chore: use target_compile_definitions instead of appending to CMAKE_CXX_FLAGS (#2713)

# Summary

Use `target_compile_definitions` instead of appending to
`CMAKE_CXX_FLAGS`

Author: jakex7

android/src/main/jni/CMakeLists.txt

@@ -7,11 +7,6 @@ set(RNS_GENERATED_DIR ${RNS_ANDROID_DIR}/build/generated)
 set(RNS_GENERATED_JNI_DIR ${RNS_GENERATED_DIR}/source/codegen/jni)
 set(RNS_GENERATED_REACT_DIR ${RNS_GENERATED_JNI_DIR}/react/renderer/components/rnsvg)
 
-string(
-  APPEND
-  CMAKE_CXX_FLAGS
-  " -DREACT_NATIVE_MINOR_VERSION=${ReactAndroid_VERSION_MINOR}")
-
 file(GLOB rnsvg_SRCS CONFIGURE_DEPENDS *.cpp ${RNS_COMMON_DIR}/react/renderer/components/rnsvg/*.cpp)
 file(GLOB rnsvg_codegen_SRCS CONFIGURE_DEPENDS ${RNS_GENERATED_REACT_DIR}/*cpp)
 
@@ -93,3 +88,9 @@ target_compile_options(
   -Wno-gnu-zero-variadic-macro-arguments
   -Wno-dollar-in-identifier-extension
 )
+
+target_compile_definitions(
+  react_codegen_rnsvg
+  PRIVATE
+  REACT_NATIVE_MINOR_VERSION=${ReactAndroid_VERSION_MINOR}
+)