Add ccache back, with fallback for sccache

cmake/tools/SetupCcache.cmake

@@ -0,0 +1,54 @@
+optionx(ENABLE_CCACHE BOOL "If ccache should be enabled" DEFAULT ON)
+
+if(NOT ENABLE_CCACHE OR CACHE_STRATEGY STREQUAL "none")
+  setenv(CCACHE_DISABLE 1)
+  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)
+  return()
+endif()
+
+set(CCACHE_ARGS CMAKE_C_COMPILER_LAUNCHER CMAKE_CXX_COMPILER_LAUNCHER)
+foreach(arg ${CCACHE_ARGS})
+  setx(${arg} ${CCACHE_PROGRAM})
+  list(APPEND CMAKE_ARGS -D${arg}=${${arg}})
+endforeach()
+
+setenv(CCACHE_DIR ${CACHE_PATH}/ccache)
+setenv(CCACHE_BASEDIR ${CWD})
+setenv(CCACHE_NOHASHDIR 1)
+
+if(CACHE_STRATEGY STREQUAL "read-only")
+  setenv(CCACHE_READONLY 1)
+elseif(CACHE_STRATEGY STREQUAL "write-only")
+  setenv(CCACHE_RECACHE 1)
+endif()
+
+setenv(CCACHE_FILECLONE 1)
+setenv(CCACHE_STATSLOG ${BUILD_PATH}/ccache.log)
+
+if(CI)
+  # FIXME: Does not work on Ubuntu 18.04
+  # setenv(CCACHE_SLOPPINESS "pch_defines,time_macros,locale,clang_index_store,gcno_cwd,include_file_ctime,include_file_mtime")
+else()
+  setenv(CCACHE_MAXSIZE 100G)
+  setenv(CCACHE_SLOPPINESS "pch_defines,time_macros,locale,random_seed,clang_index_store,gcno_cwd")
+endif()
+
+
+