Update WebKit to c8e4b57dd997 (fix Windows build)

Updates WEBKIT_VERSION to latest upstream merge.

Changes to local WebKit build support:
- Removed DerivedSources/inspector from include paths (headers already
  in PrivateHeaders/JavaScriptCore, including both caused redefinition
  errors)
- Don't define USE_MIMALLOC when building with WEBKIT_LOCAL (WebKit's
  cmakeconfig.h already defines it)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

cmake/targets/BuildBun.cmake

@@ -911,7 +911,12 @@ if(WIN32)
 endif()
 
 if(USE_MIMALLOC_AS_DEFAULT_ALLOCATOR)
-  target_compile_definitions(${bun} PRIVATE USE_MIMALLOC=1)
+  # When building with WEBKIT_LOCAL, don't define USE_MIMALLOC here since it's
+  # already defined in WebKit's cmakeconfig.h (as either 0 or 1 depending on
+  # how WebKit was built). This avoids macro redefinition errors.
+  if(NOT WEBKIT_LOCAL)
+    target_compile_definitions(${bun} PRIVATE USE_MIMALLOC=1)
+  endif()
 endif()
 
 target_compile_definitions(${bun} PRIVATE

cmake/tools/SetupWebKit.cmake

@@ -2,7 +2,7 @@ option(WEBKIT_VERSION "The version of WebKit to use")
 option(WEBKIT_LOCAL "If a local version of WebKit should be used instead of downloading")
 
 if(NOT WEBKIT_VERSION)
-  set(WEBKIT_VERSION 5ae5f07f29059c183a8db2eef2c9aabd474ec73c)
+  set(WEBKIT_VERSION c8e4b57dd997f535040d45c08b8057bad43bfabd)
 endif()
 
 string(SUBSTRING ${WEBKIT_VERSION} 0 16 WEBKIT_VERSION_PREFIX)
@@ -34,7 +34,9 @@ if(WEBKIT_LOCAL)
       ${WEBKIT_PATH}/bmalloc/Headers
       ${WEBKIT_PATH}/WTF/Headers
       ${WEBKIT_PATH}/JavaScriptCore/PrivateHeaders/JavaScriptCore
-      ${WEBKIT_PATH}/JavaScriptCore/DerivedSources/inspector
+      # Note: DerivedSources/inspector is NOT included here because all inspector
+      # headers are already in PrivateHeaders/JavaScriptCore. Including both paths
+      # causes "redefinition" errors since the same headers exist in both locations.
     )
   endif()