FB. Build System. New names for variables: FB_BUILD__xxx.

ROOT_TEMP_DIR2 -> FB_BUILD__ROOT_TEMP_DIR
FB_COMPILE_LOG_DIR -> FB_BUILD__COMPILE_LOG_DIR
FB_ICU_SOURCE_BIN2 -> FB_BUILD__ICU_SOURCE_BIN
FB_TEMP_DIR2 -> FB_BUILD__TEMP_DIR
FB_OUT_DIR2 -> FB_BUILD__OUT_DIR