Also apply Clang-specific flags when the compiler is AppleClang
https://github.com/DaveGamble/cJSON/pull/773
--- CMakeLists.txt.orig	2023-07-04 22:22:19.000000000 -0500
+++ CMakeLists.txt	2023-07-09 22:00:44.000000000 -0500
@@ -17,7 +17,7 @@
 include(CheckCCompilerFlag)
 option(ENABLE_CUSTOM_COMPILER_FLAGS "Enables custom compiler flags" ON)
 if (ENABLE_CUSTOM_COMPILER_FLAGS)
-    if (("${CMAKE_C_COMPILER_ID}" STREQUAL "Clang") OR ("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU"))
+    if (("${CMAKE_C_COMPILER_ID}" MATCHES "Clang") OR ("${CMAKE_C_COMPILER_ID}" STREQUAL "GNU"))
         list(APPEND custom_compiler_flags
             -std=c89
             -pedantic