ZX Spectrum Build Requires Multiple Invocations of waf

[ajbowen249]

This is also mentioned in the readme, but for sake of process, here's a formal issue.

When building with zx_spectrum included in --platforms, the initial invocation of waf will fail with an error like:

Build failed
Traceback (most recent call last):
  File "mol\dde\waf3-2.1.1-073e1606e6ae84d01a398086bd4053ad\waflib\Context.py", line 182, in exec_command
    ret,out,err=Utils.run_process(cmd,kw,cargs)
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "mol\dde\waf3-2.1.1-073e1606e6ae84d01a398086bd4053ad\waflib\Utils.py", line 614, in run_process
    return run_prefork_process(cmd,kwargs,cargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "mol\dde\waf3-2.1.1-073e1606e6ae84d01a398086bd4053ad\waflib\Utils.py", line 549, in run_prefork_process
    proc.stdin.write(obj)
BrokenPipeError: [Errno 32] Broken pipe

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "mol\dde\waf3-2.1.1-073e1606e6ae84d01a398086bd4053ad\waflib\Task.py", line 179, in process
    ret=self.run()
        ^^^^^^^^^^
  File "mol\dde\tools\dde_tasks.py", line 142, in run
    return self.exec_command([
           ^^^^^^^^^^^^^^^^^^^
  File "mol\dde\waf3-2.1.1-073e1606e6ae84d01a398086bd4053ad\waflib\Task.py", line 172, in exec_command
    return self.generator.bld.exec_command(cmd,**kw)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "mol\dde\waf3-2.1.1-073e1606e6ae84d01a398086bd4053ad\waflib\Context.py", line 184, in exec_command
    raise Errors.WafError('Execution failure: %s'%str(e),ex=e)
waflib.Errors.WafError: Execution failure: [Errno 32] Broken pipe

Running waf again will be successful. Until this is fixed, zx_spectrum support is not in --platforms by default.