bootstrap: Clarify name of configured source directory

Rename CMAKE_ROOT_DIR to CMAKE_BOOTSTRAP_SOURCE_DIR to clarify both that
it is only for bootstrap and that it refers to the source directory.

Source/cmSystemTools.cxx

@@ -2215,7 +2215,7 @@ void cmSystemTools::FindCMakeResources(const char* argv0)
     }
 #else
   // Bootstrap build knows its source.
-  cmSystemToolsCMakeRoot = CMAKE_ROOT_DIR;
+  cmSystemToolsCMakeRoot = CMAKE_BOOTSTRAP_SOURCE_DIR;
 #endif
 }
 

bootstrap

@@ -1474,9 +1474,9 @@ fi
 # When bootstrapping on MinGW with MSYS we must convert the source
 # directory to a windows path.
 if ${cmake_system_mingw}; then
-    cmake_root_dir=`cd "${cmake_source_dir}"; pwd -W`
+    CMAKE_BOOTSTRAP_SOURCE_DIR=`cd "${cmake_source_dir}"; pwd -W`
 else
-    cmake_root_dir="${cmake_source_dir}"
+    CMAKE_BOOTSTRAP_SOURCE_DIR="${cmake_source_dir}"
 fi
 
 # Write CMake version
@@ -1484,7 +1484,7 @@ cmake_report cmVersionConfig.h${_tmp} "#define CMake_VERSION_MAJOR ${cmake_versi
 cmake_report cmVersionConfig.h${_tmp} "#define CMake_VERSION_MINOR ${cmake_version_minor}"
 cmake_report cmVersionConfig.h${_tmp} "#define CMake_VERSION_PATCH ${cmake_version_patch}"
 cmake_report cmVersionConfig.h${_tmp} "#define CMake_VERSION \"${cmake_version}\""
-cmake_report cmConfigure.h${_tmp} "#define CMAKE_ROOT_DIR \"${cmake_root_dir}\""
+cmake_report cmConfigure.h${_tmp} "#define CMAKE_BOOTSTRAP_SOURCE_DIR \"${CMAKE_BOOTSTRAP_SOURCE_DIR}\""
 cmake_report cmConfigure.h${_tmp} "#define CMAKE_DATA_DIR \"/bootstrap-not-insalled\""
 cmake_report cmConfigure.h${_tmp} "#define CMAKE_BOOTSTRAP"