genccode, toolutil: C code generation doesn't allow to override the entry point

Hi,

This bug is to report that the genccode tool cannot generate C code with an overridden entry point.

Example invocation:

This should generate a .c file containing the equivalent code as when adding e.g. -a gcc-mingw64; however, the former has the following preamble:

whereas the assembly file is correctly generated:

Using -n is of no effect, as it only prepends the entry point instead of replacing it.

The cause of this bug is that writeCCode simply does not take optEntryPoint as a parameter.