Get warning I don't know how to fix : main.c:95:: warning: (1518) direct function call mad

You don't need the 'extern'

should be
void receiver_init(void) {
you need the void in the actual function, not just the header

This declaration

void receiver_init()

can accept any arguments. As others said, the correct declaration is

void receiver_init(void)

which is a function without arguments.

rikotech
I think the compiler could imply void argument list from the empty parenthesis.

With an empty () it is telling the compiler not to do any checks on the parameters list.  That is, this

  receiver_init();

and this

  receiver_init(foo,bar,baz);

will work.
 

I do trust the compiler does not "imply" anything, but follows strict rules.

Compilers do not even "try some educated guess" if your code is not absolutely clear and free from errors. Instead they simply throw warnings and errors.

Not exactly my experience.
Once MPLAB/XC8 threw a mysterios error. Now I tend to sometimes have doxygen (resp. Clang) check my code as well: gives useful additional insights.

I just got this error in MPLABX5.20, XC8 2.05
 
In the MCC-generated code (ADCC.C/H), the function 
bool ADCC_IsConversionDone()
is defined.
 
Making this
bool ADCC_IsConversionDone(void)
fixes the error.
 
Buggy tools? Now there's a novelty.

Section 6.11.6 of the C99 standards says that it is a "future language direction", but for now...

6.7.5.3 Function declarators (including prototypes)
4 - After adjustment, the parameters in a parameter type list in a function declarator that is
part of a definition of that function shall not have incomplete type.

Edit/

Also
C99 Annex J.2 Undefined behavior

For a call to a function without a function prototype in scope, the number of arguments does not equal the number of parameters (6.5.2.2).
For call to a function without a function prototype in scope where the function is defined with a function prototype, either the prototype ends with an ellipsis or the types of the arguments after promotion are not compatible with the types of the parameters (6.5.2.2).
For a call to a function without a function prototype in scope where the function is not defined with a function prototype, the types of the arguments after promotion are not compatible with those of the parameters after promotion (with certain exceptions) (6.5.2.2).