public boolean hasCustomCallingConvention() {
		return (flagByte & HAS_CUSTOM_CALLING_CONVENTION) != 0;
	}
Indicates if has custom calling convention.
<p>
Not sure how this is weighed against a function spec that has a valid calling convention,
when a function symbol will have both this {@link ProcedureFlags} and a
{@link AbstractProcedureMsType} function spec with the calling convention.
@return true if has custom calling convention
Ghidra/Features/PDB/src/main/java/ghidra/app/util/bin/format/pdb2/pdbreader/symbol/ProcedureFlags.java