[common] use abi::__cxa_demangle for demangling using the system's glibcxx/libc++ (#3894)

most stdlibc++ already provide this functionality out of the box, very consistently and well implemented (usually)

my main irk is that the llvm itanium demangle is totally unescesary when there is a perfectly stable, tested and well documented equivalent functionality in the standard stdc++ provided in most UNIX oses

its mostly to reduce binary size by a very thin margin, but he stdc++ is more than capable of doing he same behaviour we use a dpeendency for

for mingw or such howeger,, demangling becomies trickier so we have to exclude windows entirely because well windows likes to do things differently dont they

Signed-off-by: lizzie <lizzie@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3894
Reviewed-by: crueter <crueter@eden-emu.dev>
Reviewed-by: MaranBr <maranbr@eden-emu.dev>

CMakeModules/FindLLVM.cmake

@@ -1,3 +1,6 @@
+# SPDX-FileCopyrightText: Copyright 2026 Eden Emulator Project
+# SPDX-License-Identifier: GPL-3.0-or-later
+
 # SPDX-FileCopyrightText: 2023 Alexandre Bouvier <contact@amb.tf>
 #
 # SPDX-License-Identifier: GPL-3.0-or-later
@@ -13,7 +16,8 @@ endif()
 include(FindPackageHandleStandardArgs)
 find_package_handle_standard_args(LLVM HANDLE_COMPONENTS CONFIG_MODE)
 
-if (LLVM_FOUND AND LLVM_Demangle_FOUND AND NOT TARGET LLVM::Demangle)
+# Demangle only for Windows targets
+if (WIN32 AND LLVM_FOUND AND LLVM_Demangle_FOUND AND NOT TARGET LLVM::Demangle)
     add_library(LLVM::Demangle INTERFACE IMPORTED)
     target_compile_definitions(LLVM::Demangle INTERFACE ${LLVM_DEFINITIONS})
     target_include_directories(LLVM::Demangle INTERFACE ${LLVM_INCLUDE_DIRS})