SDL: Use bundled LibUSB when desirable

Previously, SDL would `find_package(libusb)` which would actually overwrite the user preference in the case where both USE_SYSTEM_LIBUSB and USE_SYSTEM_SDL were OFF. This coincidentally also allows SDL to use libusb on Windows.

CMakeLists.txt

@@ -582,10 +582,6 @@ if(UNIX)
   add_definitions(-DUSE_MEMORYWATCHER=1)
 endif()
 
-if(ENABLE_SDL)
-  dolphin_find_optional_system_library(SDL3 Externals/SDL 3.2.0)
-endif()
-
 if(ENABLE_ANALYTICS)
   message(STATUS "Enabling analytics collection (subject to end-user opt-in)")
   add_definitions(-DUSE_ANALYTICS=1)
@@ -712,6 +708,10 @@ if(NOT ANDROID)
   add_definitions(-D__LIBUSB__)
 endif()
 
+if(ENABLE_SDL)
+  dolphin_find_optional_system_library(SDL3 Externals/SDL 3.2.0)
+endif()
+
 dolphin_find_optional_system_library(SFML Externals/SFML 3.0 COMPONENTS Network System)
 
 if(USE_UPNP)

Externals/SDL/CMakeLists.txt

@@ -20,6 +20,11 @@ if(CCACHE_BIN)
   set(CCACHE_BINARY ${CCACHE_BIN})
 endif()
 
+if(LibUSB_TYPE STREQUAL Bundled)
+  set(LibUSB_FOUND TRUE)
+  set(SDL_HIDAPI_LIBUSB_SHARED OFF)
+endif()
+
 add_subdirectory(SDL)
 
 if (TARGET SDL3)

Externals/libusb/CMakeLists.txt

@@ -125,4 +125,15 @@ check_include_files(sys/timerfd.h HAVE_TIMERFD)
 check_include_files(unistd.h HAVE_UNISTD_H)
 
 configure_file(config.h.in config.h)
-add_library(LibUSB::LibUSB ALIAS usb)
+
+# We don't create an ALIAS here so that dependencies (SDL) that try_compile libusb
+# don't fail due to LibUSB::LibUSB being an alias target
+add_library(LibUSB::LibUSB INTERFACE IMPORTED GLOBAL)
+target_link_libraries(LibUSB::LibUSB
+  INTERFACE
+    usb
+)
+target_include_directories(LibUSB::LibUSB
+  INTERFACE
+    ${CMAKE_CURRENT_SOURCE_DIR}/libusb/libusb
+)