make sccache available for all cmake users, not only CI

if you have it in your path, the build will use

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -201,9 +201,7 @@ jobs:
         run: |
           # sccache can only cache MSVC objects when the debug information is embedded
           # in them (/Z7) instead of collected in a shared PDB (/Zi, the CMake default)
-          cmake -S . -B build -GNinja -DCMAKE_BUILD_TYPE=RelWithDebInfo -DApplications="$Env:JA2Application" `
-            -DCMAKE_POLICY_DEFAULT_CMP0141=NEW -DCMAKE_MSVC_DEBUG_INFORMATION_FORMAT=Embedded `
-            -DCMAKE_C_COMPILER_LAUNCHER=sccache -DCMAKE_CXX_COMPILER_LAUNCHER=sccache
+          cmake -S . -B build -GNinja -DCMAKE_BUILD_TYPE=RelWithDebInfo -DApplications="$Env:JA2Application"
       - name: Build
         run: |
           cmake --build build/ -- -v

CMakeLists.txt

@@ -1,7 +1,23 @@
 cmake_minimum_required(VERSION 3.20)
 
+# /Z7 embedded debug info so objects are self-contained and sccache-able.
+# CMP0141 is a 3.25 policy; our floor is 3.20, so opt in explicitly where known.
+if(POLICY CMP0141)
+  cmake_policy(SET CMP0141 NEW)
+endif()
+
 project(ja2)
 
+option(USE_SCCACHE "Cache compiled objects with sccache if installed" ON)
+if(USE_SCCACHE)
+  find_program(SCCACHE_PROGRAM sccache)
+  if(SCCACHE_PROGRAM)
+    message(STATUS "Using sccache: ${SCCACHE_PROGRAM}")
+    set(CMAKE_C_COMPILER_LAUNCHER   "${SCCACHE_PROGRAM}")
+    set(CMAKE_CXX_COMPILER_LAUNCHER "${SCCACHE_PROGRAM}")
+  endif()
+endif()
+
 include(cmake/CopyUserPresetTemplate.cmake)
 CopyUserPresetTemplate()
 
@@ -40,6 +56,9 @@ set(usingMsBuild $<STREQUAL:${CMAKE_VS_PLATFORM_NAME},Win32>)
 # lua51.lib and lua51.vc9.lib have been built with /MTx, so we must as well
 # TODO: build our own Lua 5.1.2 from source so we can use whichever
 set(CMAKE_MSVC_RUNTIME_LIBRARY "MultiThreaded$<$<CONFIG:Debug>:Debug>")
+# make Debug builds /Z7 instead of /Zi so they can be sccache'd
+set(CMAKE_MSVC_DEBUG_INFORMATION_FORMAT
+  "$<$<CONFIG:Debug,RelWithDebInfo>:Embedded>")
 
 add_compile_definitions(CINTERFACE XML_STATIC VFS_STATIC VFS_WITH_SLF VFS_WITH_7ZIP _CRT_SECURE_NO_DEPRECATE)
 include_directories(