[publish images] Remove sccache, use ccache only (#25682)

## Summary
- Remove sccache support entirely, use ccache only
- Missing ccache no longer fails the build (just skips caching)
- Remove S3 distributed cache support

## Changes
- Remove `cmake/tools/SetupSccache.cmake` and S3 distributed cache
support
- Simplify `CMakeLists.txt` to only use ccache
- Update `SetupCcache.cmake` to not fail when ccache is missing
- Replace sccache with ccache in bootstrap scripts (sh, ps1)
- Update `.buildkite/Dockerfile` to install ccache instead of sccache
- Update `flake.nix` and `shell.nix` to use ccache
- Update documentation (CONTRIBUTING.md, contributing.mdx,
building-windows.mdx)
- Remove `scripts/build-cache/` directory (was only for sccache S3
access)

## Test plan
- [x] Build completes successfully with `bun bd`

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Bot <claude-bot@bun.sh>
Co-authored-by: Claude <noreply@anthropic.com>

cmake/tools/SetupCcache.cmake

@@ -5,18 +5,12 @@ if(NOT ENABLE_CCACHE OR CACHE_STRATEGY STREQUAL "none")
   return()
 endif()
 
-if (CI AND NOT APPLE)
-  setenv(CCACHE_DISABLE 1)
-  return()
-endif()
 
 find_command(
   VARIABLE
     CCACHE_PROGRAM
   COMMAND
     ccache
-  REQUIRED
-    ${CI}
 )
 
 if(NOT CCACHE_PROGRAM)

cmake/tools/SetupSccache.cmake

@@ -1,123 +0,0 @@
-# Setup sccache as the C and C++ compiler launcher to speed up builds by caching
-if(CACHE_STRATEGY STREQUAL "none")
-  return()
-endif()
-
-set(SCCACHE_SHARED_CACHE_REGION "us-west-1")
-set(SCCACHE_SHARED_CACHE_BUCKET "bun-build-sccache-store")
-
-# Function to check if the system AWS credentials have access to the sccache S3 bucket.
-function(check_aws_credentials OUT_VAR)
-  # Install dependencies first
-  execute_process(
-    COMMAND ${BUN_EXECUTABLE} install --frozen-lockfile
-    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}/scripts/build-cache
-    RESULT_VARIABLE INSTALL_EXIT_CODE
-    OUTPUT_VARIABLE INSTALL_OUTPUT
-    ERROR_VARIABLE INSTALL_ERROR
-  )
-
-  if(NOT INSTALL_EXIT_CODE EQUAL 0)
-    message(FATAL_ERROR "Failed to install dependencies in scripts/build-cache\n"
-      "Exit code: ${INSTALL_EXIT_CODE}\n"
-      "Output: ${INSTALL_OUTPUT}\n"
-      "Error: ${INSTALL_ERROR}")
-  endif()
-
-  # Check AWS credentials
-  execute_process(
-    COMMAND
-      ${BUN_EXECUTABLE}
-      run
-      have-access.ts
-      --bucket ${SCCACHE_SHARED_CACHE_BUCKET}
-      --region ${SCCACHE_SHARED_CACHE_REGION}
-    WORKING_DIRECTORY
-      ${CMAKE_SOURCE_DIR}/scripts/build-cache
-    RESULT_VARIABLE HAVE_ACCESS_EXIT_CODE
-  )
-
-  if(HAVE_ACCESS_EXIT_CODE EQUAL 0)
-    set(HAS_CREDENTIALS TRUE)
-  else()
-    set(HAS_CREDENTIALS FALSE)
-  endif()
-
-  set(${OUT_VAR} ${HAS_CREDENTIALS} PARENT_SCOPE)
-endfunction()
-
-# Configure sccache to use the local cache only.
-function(sccache_configure_local_filesystem)
-  unsetenv(SCCACHE_BUCKET)
-  unsetenv(SCCACHE_REGION)
-  setenv(SCCACHE_DIR "${CACHE_PATH}/sccache")
-endfunction()
-
-# Configure sccache to use the distributed cache (S3 + local).
-function(sccache_configure_distributed)
-  setenv(SCCACHE_BUCKET "${SCCACHE_SHARED_CACHE_BUCKET}")
-  setenv(SCCACHE_REGION "${SCCACHE_SHARED_CACHE_REGION}")
-  setenv(SCCACHE_DIR "${CACHE_PATH}/sccache")
-endfunction()
-
-function(sccache_configure_environment_ci)
-  if(CACHE_STRATEGY STREQUAL "auto" OR CACHE_STRATEGY STREQUAL "distributed")
-    check_aws_credentials(HAS_AWS_CREDENTIALS)
-    if(HAS_AWS_CREDENTIALS)
-      sccache_configure_distributed()
-      message(NOTICE "sccache: Using distributed cache strategy.")
-    else()
-      message(FATAL_ERROR "CI CACHE_STRATEGY is set to '${CACHE_STRATEGY}', but no valid AWS "
-        "credentials were found. Note that 'auto' requires AWS credentials to access the shared "
-        "cache in CI.")
-    endif()
-  elseif(CACHE_STRATEGY STREQUAL "local")
-    # We disallow this because we want our CI runs to always used the shared cache to accelerate
-    # builds.
-    # none, distributed and auto are all okay.
-    #
-    # If local is configured, it's as good as "none", so this is probably user error.
-    message(FATAL_ERROR "CI CACHE_STRATEGY is set to 'local', which is not allowed.")
-  endif()
-endfunction()
-
-function(sccache_configure_environment_developer)
-  # Local environments can use any strategy they like. S3 is set up in such a way so as to clean
-  # itself from old entries automatically.
-  if (CACHE_STRATEGY STREQUAL "auto" OR CACHE_STRATEGY STREQUAL "local")
-    # In the local environment, we prioritize using the local cache. This is because sccache takes
-    # into consideration the whole absolute path of the files being compiled, and it's very
-    # unlikely users will have the same absolute paths on their local machines.
-    sccache_configure_local_filesystem()
-    message(NOTICE "sccache: Using local cache strategy.")
-  elseif(CACHE_STRATEGY STREQUAL "distributed")
-    check_aws_credentials(HAS_AWS_CREDENTIALS)
-    if(HAS_AWS_CREDENTIALS)
-      sccache_configure_distributed()
-      message(NOTICE "sccache: Using distributed cache strategy.")
-    else()
-      message(FATAL_ERROR "CACHE_STRATEGY is set to 'distributed', but no valid AWS credentials "
-        "were found.")
-    endif()
-  endif()
-endfunction()
-
-find_command(VARIABLE SCCACHE_PROGRAM COMMAND sccache REQUIRED ${CI})
-if(NOT SCCACHE_PROGRAM)
-  message(WARNING "sccache not found. Your builds will be slower.")
-  return()
-endif()
-
-set(SCCACHE_ARGS CMAKE_C_COMPILER_LAUNCHER CMAKE_CXX_COMPILER_LAUNCHER)
-foreach(arg ${SCCACHE_ARGS})
-  setx(${arg} ${SCCACHE_PROGRAM})
-  list(APPEND CMAKE_ARGS -D${arg}=${${arg}})
-endforeach()
-
-setenv(SCCACHE_LOG "info")
-
-if (CI)
-  sccache_configure_environment_ci()
-else()
-  sccache_configure_environment_developer()
-endif()