Support multiple chars shorthand eg: -ff file --filefrom file

[timandy]

Support multiple chars shorthand.
eg:
-ff file
--filefrom file

some commit cherry-picked from #175 .

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[brandon1024]

I'm not sure these changes really fit into the spirit of the pflag library. The changes proposed here deviate from POSIX and introduce ambiguities. If you want something like this, I would almost recommend sticking to the standard flag library which allows you do handle flags like this more easily without deviating from POSIX conventions.

flag.StringVar(&from, "ff", "", "usage")
flag.StringVar(&from, "fromfile", "", "usage")

[timandy]

go asm use no-standard flag, I want to use this lib resolve asm args, befor pass to it.

.\asm.exe --help
usage: asm [options] file.s ...
Flags:
 -D value
       predefined symbol with optional simple value -D=identifier=value; can be set multiple times
 -I value
       include directory; can be set multiple times
 -S    print assembly and machine code
 -V    print version and exit
 -d value
       enable debugging settings; try -d help
 -debug
       dump instructions as they are parsed
 -dynlink
       support references to Go symbols defined in other shared libraries
 -e    no limit on number of errors reported
 -gensymabis
       write symbol ABI information to output file, don't assemble
 -linkshared
       generate code that will be linked against Go shared libraries
 -o string
       output file; default foo.o for /a/b/c/foo.s as first argument
 -p string
       set expected package import to path (default "<unlinkable>")
 -shared
       generate code that can be linked into a shared library
 -spectre list
       enable spectre mitigations in list (all, ret)
 -trimpath string
       remove prefix from recorded source file paths
 -v    print debug output

[brandon1024]

All standard go tooling (build, test, asm, etc) use the flag stdlib. This was an explicit design choice by the Go developers, and this will not be changed. If you need go-style flag parsing, use the stdlib. If you want POSIX flags, use pflag.

[brandon1024]

This might be helpful depending on what you're trying to do:

https://github.com/spf13/pflag?tab=readme-ov-file#supporting-go-flags-when-using-pflag