Fix A2168 - General failure using 64-bit MSVC

[madebr]

When assembling this file called lin64_1.asm:

;--- "hello world" for 64-bit Linux, using SYSCALL.
;--- assemble: JWasm -elf64 -Fo=Lin64_1.o Lin64_1.asm
;--- link:     gcc Lin64_1.o -o Lin64_1

stdout    equ 1
SYS_WRITE equ 1
SYS_EXIT  equ 60

    .data

string  db 10,"Hello, world!",10

    .code

_start:
    mov edx, sizeof string
    mov rsi, offset string
    mov edi, stdout
    mov eax, SYS_WRITE
    syscall
    mov eax, SYS_EXIT
    syscall

    end _start

using the command:

jwasm.exe -elf64 -Fo=lin64_1.o lin64_1.asm

jwasm of current master fails with the following message:

JWasm v2.15pre, Jan 21 2021, Masm-compatible assembler.
Portions Copyright (c) 1992-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.

C:\Users\maarten\source\repos\conan-center-index\recipes\jwasm\all\test_package\Lin64_1.asm: 24 lines, 2 passes, 2 ms, 0 warnings, 0 errors
Error A2168: General Failure

With the patch of this pr, the message becomes:

JWasm v2.15pre, Jan 21 2021, Masm-compatible assembler.
Portions Copyright (c) 1992-2002 Sybase, Inc. All Rights Reserved.
Source code is available under the Sybase Open Watcom Public License.

C:\Users\maarten\source\repos\conan-center-index\recipes\jwasm\all\test_package\Lin64_1.asm: 24 lines, 2 passes, 3 ms, 0 warnings, 0 errors

FYI: We detected this problem while trying to add a jwasm to conan-center-index at https://github.com/conan-io/conan-center-index/pull/4321. The first version of the build recipe is to use jwasm at https://github.com/JWasm/JWasm, but that fork is stale. Can you comment on the relation between this fork and the other?

The other fork uses cmake, is there any reason that isn't used here? We, at conan-center, kinda like cmake because it lets us build packages uniformly on all platform. When using cmake, there is only one unified build script and no need to use multiple make script with each script having its issues.

[Baron-von-Riedesel]

bug confirmed. "Obviously" a pointer (as returned by fopen()) won't fit in a long in Win64.

Can you comment on the relation between this fork and the other?

I'm the "original" author of jwasm.

The other fork uses cmake, is there any reason that isn't used here?

I'd like to use as little tools as possible to create jwasm.