[WIP] gh-105323: Suppress function pointer warning by type casting

[corona10]

• Issue: Incompatible function pointer types assigning to 'Function *' at readline module #105323

[corona10]

Type definitions from the macOS readline.h

/* typedefs */
typedef int	  Function(const char *, int);
typedef void	  VFunction(void);
typedef void	  VCPFunction(char *);
typedef char	 *CPFunction(const char *, int);
typedef char	**CPPFunction(const char *, int, int);
typedef char     *rl_compentry_func_t(const char *, int);
typedef int	  rl_command_func_t(int, int);

[corona10]

I will discover a better approach than this PR..

[erlend-aasland]

Type definitions from the macOS readline.h

Confirming this on my box:

$ locate readline.h | xargs grep -n "typedef.*\<Function"
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/editline/readline.h:40:typedef int	  Function(const char *, int);
/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/readline/readline.h:40:typedef int	  Function(const char *, int);
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/include/editline/readline.h:40:typedef int	  Function(const char *, int);
/Library/Developer/CommandLineTools/SDKs/MacOSX12.3.sdk/usr/include/readline/readline.h:40:typedef int	  Function(const char *, int);
/Library/Developer/CommandLineTools/SDKs/MacOSX13.3.sdk/usr/include/editline/readline.h:40:typedef int	  Function(const char *, int);
/Library/Developer/CommandLineTools/SDKs/MacOSX13.3.sdk/usr/include/readline/readline.h:40:typedef int	  Function(const char *, int);