fix: add comprehensive workaround for conda libc++ on macOS

The conda-provided libc++ on macOS has compatibility issues with
ptrdiff_t and other standard library types due to _LIBCPP_USING_IF_EXISTS
failing to resolve types from the global namespace.

Changes:
- Include stddef.h (C header) before C++ headers to ensure types are defined
- Add _LIBCPP_DISABLE_AVAILABILITY flag on macOS to disable availability checks
  that can conflict with conda environments

This resolves the 'reference to unresolved using declaration' error for
ptrdiff_t in char_traits.h when building with conda on macOS.

References:
- conda/conda#11196
- llvm/llvm-project#54233

Author: sameeul

src/filepattern/cpp/CMakeLists.txt

@@ -60,6 +60,11 @@ if(JAVA_BINDING)
 	add_compile_definitions(JAVA_BINDING)
 endif()
 
+# Workaround for conda libc++ compatibility on macOS
+if(APPLE)
+	add_compile_definitions(_LIBCPP_DISABLE_AVAILABILITY)
+endif()
+
 #==== Source files
 set(SOURCE  pattern.cpp
 			interface/filepattern.cpp

src/filepattern/cpp/pattern.hpp

@@ -10,6 +10,11 @@
  */
 
 #pragma once
+
+// Workaround for conda libc++ on macOS: include C headers before C++ headers
+// to ensure ptrdiff_t and other types are properly defined
+#include <stddef.h>
+
 #include <cstddef>
 #include <string>
 #include <iostream>