Fix compile crash when using CALL in #emit

This fixes a crash when calling a function with the CALL instruction in #emit.

Instead of merely writing a symbol's address to the .asm file we check
if we are in a CALL instruction, and if so we output the function's name
rather than its address.

See 7) here: http://forum.sa-mp.com/showthread.php?t=355877

--------- test code --------

foo() {}

main() {
	#emit call foo
}

----- end of test code -----
Fix #emit SYSREQ.C generating wrong native index for unused natives

This commit fixes a bug where the compiler generated incorrect native
index in assembly code for natives invoked via #emit sysreq.c and not
called elsewhere with the normal syntax.

See 4) here: http://forum.sa-mp.com/showthread.php?t=355877

--------- test code --------

native print(const s[]);
native printf(const format[], ...);

main() {
	new string[] = "hi there!";
	printf(string);
	#emit push.s string
	#emit push.c 4
	#emit sysreq.c print
	#emit sysreq.c printf
}

----- end of test code -----