Fix parameter and return types for dynamically called functions

[richardlford]

Calls to dynamically-linked functions go through the procedure linkage
table (PLT). RetDec turns a PLT entry into a function, say
malloc@plt, that appears to do nothing but call the external function,
say malloc (though the assembly code will do a jump rather than a
call). User code that logically wants to call malloc instead calls
malloc@plt (and sets up arguments as if calling malloc). The
malloc@plt code first jumps to the dynamic linker which modifies it so
that subsequent calls to malloc@plt will jump directly to malloc. We
say that malloc@plt wraps malloc. The call to malloc in malloc@plt
will not have any arguments setup, so malloc will appear to have
no parameters or returns (unless that information is provided by
link-time-information, debug information, or name demangling), but it
needs to have the same parameter types and return type as
malloc@plt. The propagateWrapped methods copy the argument information
from the DataFlowEntry of the wrapping function to the wrapped
function. Then, when the calls to the wrapping function are inlined
(in connectWrappers), effectively the call to the wrapping function is
changed into a call to the wrapped function.

The motivation for this change is the programs that analyze the
output of RetDec (either the C code, or the LLVM code) want to
recognize library functions and treat them specially. This
change makes it so that the library function names are used
directly (rather than the plt version) and they are passed
their parameters correctly.

[richardlford]

@PeterMatula, could you please review this change. This change is smaller and simpler than my previous attempt. In addition, the regression tests all pass (at least all I was able to run), provided the adjustments in PR avast/retdec-regression-tests#117 (comment) are made.

[PeterMatula]

Thanks a lot @richardlford, looks good and it works for me locally. I will look at other PRs tomorrow.