mprotect missing from type libraries

[xusheng6]

A user reported that we are missing the type library info for the mprotect function:

This can be verified from the API as well:

>>> type_lib = bv.platform.get_type_libraries_by_name('libc_x86_64.so.6')[0]
>>> bv.import_library_object('mprotect', type_lib)

[xusheng6]

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