[libmicrohttpd] Problems with libmicrohttpd.a on a gnu_linux-armeabihf platform

[Bob Furber]

 I have a program using mictohttpd that works very well on a 64 bit 
Linux PC, but I am having a devil of a time with mictohttpd in my 
attempt to port this program to a gnu-linux-eabihf platform. I get the 
same error when calling MHD_create_response_from_callback(), whether I 
use a precompiled gnu-linux-eabihf libmicrohttpd.a or, whether I build 
it myself on the Arm platform:

error: invalid conversion from ‘long int (*)(void*, uint64_t, char*, 
size_t) {aka long int (*)(void*, long long unsigned int, char*, unsigned 
int)}’ to ‘MHD_ContentReaderCallback {aka int (*)(void*, long long 
unsigned int, char*, unsigned int)}’ [-fpermissive]

It would appear there is a problem on the armhf with the 
MHD_ContentReaderCallback function passed as a parameter to 
MHD_create_response_from_callback() returning a long int instead of a 
type ssize_t as per its prototype. It appears that in the LinuxPC 
version, ssize_t was equivalent to a long int, whereas, on the armhf 
version, it is equivalent to an int.

However, changing the MHD_ContentReaderCallback function to return an 
int or a ssize_t results in a ton of “undefined reference to `MHD_xxx'” 
errors.

I should also mention that the MHD_create_response_from_callback() 
declaration in microhttpd.h displays this obscure error:

initializing argument 3 of ‘MHD_Response* 
MHD_create_response_from_callback(uint64_t, size_t, 
MHD_ContentReaderCallback, void*, MHD_ContentReaderFreeCallback)’ 
[-fpermissive]

At my wits' end...