[cmake] more modules, general "cleanup" (#3126)

Successor to that old MoltenVK PR. Does a lot of cleanups within root CMakeLists.txt, hands over MoltenVK and VulkanValidationLayers to CPMUtil, and separates out common operations into my modules.

Hopefully reduces the monstrosity that is root CMakeLists.txt. Please test:

- builds on all platforms
- VulkanValidationLayers

Signed-off-by: crueter <crueter@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3126
Reviewed-by: Lizzie <lizzie@eden-emu.dev>
Reviewed-by: CamilleLaVey <camillelavey99@gmail.com>

externals/cmake-modules/FasterLinker.cmake

@@ -0,0 +1,58 @@
+# SPDX-FileCopyrightText: Copyright 2025 crueter
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+## FasterLinker ##
+
+# This finds a faster linker for your compiler, if available.
+# Only really tested on Linux. I would not recommend this on MSYS2.
+
+#[[
+    search order:
+    - gold (GCC only) - the best, generally, but not packaged anymore
+    - mold (GCC only) - generally does well on GCC
+    - lld - preferred on clang
+    - bfd - the final fallback
+    - If none are found (macOS uses ld.prime, etc) just use the default linker
+]]
+
+# This module is based on the work of Yuzu, specifically Liam White,
+# and later extended by crueter.
+
+if (CMAKE_CXX_COMPILER_ID STREQUAL "GNU")
+    set(CXX_GCC ON)
+endif()
+
+find_program(LINKER_BFD bfd)
+if (LINKER_BFD)
+    set(LINKER bfd)
+endif()
+
+find_program(LINKER_LLD lld)
+if (LINKER_LLD)
+    set(LINKER lld)
+endif()
+
+if (CXX_GCC)
+    find_program(LINKER_MOLD mold)
+    if (LINKER_MOLD AND CMAKE_CXX_COMPILER_VERSION VERSION_GREATER_EQUAL "12.1")
+        set(LINKER mold)
+    endif()
+
+    find_program(LINKER_GOLD gold)
+    if (LINKER_GOLD)
+        set(LINKER gold)
+    endif()
+endif()
+
+if (LINKER)
+    message(NOTICE "[FasterLinker] Selecting ${LINKER} as linker")
+    add_link_options("-fuse-ld=${LINKER}")
+else()
+    message(WARNING "[FasterLinker] No faster linker found--using default")
+endif()
+
+if (LINKER STREQUAL "lld" AND CXX_GCC)
+    message(WARNING
+        "[FasterLinker] Using lld on GCC may cause issues "
+        "with certain LTO settings.")
+endif()