Function mbedtls_platform_support::self_test::enable  
source · pub unsafe fn enable(
    rand: fn() -> c_int,
    log: Option<unsafe fn(_: *const c_char)>
)Expand description
Set callback functions to enable the MbedTLS self tests.
rand only needs to be set on platforms that don’t have a rand() 
function in libc. log only needs to be set when using no_std, i.e. 
the std feature of this create is not enabled. If neither function 
needs to be set, you don’t have to call enable().
Safety
The caller needs to ensure this function is not called while any other function in this module is called.