include: Sync lto-symtab.h and plugin-api.h with GCC

Fix comma at end of enumerator list seen with -std=c++98.

	* plugin-api.h (enum ld_plugin_symbol_type): Remove
	comma after last value of an enum.
	* lto-symtab.h (enum gcc_plugin_symbol_type): Likewise.

(cherry picked from commit e3b1fa32)