[MacPorts] #51367: gcc6: add OpenACC NVIDIA offload compilers

[MacPorts]

#51367: gcc6: add OpenACC NVIDIA offload compilers
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  Reporter:  thomasdeakin@…  |      Owner:  mww@…
      Type:  enhancement     |     Status:  new
  Priority:  Normal          |  Milestone:
 Component:  ports           |    Version:
Resolution:                  |   Keywords:
      Port:  gcc6            |
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Comment (by thomasdeakin@…):

 It's pretty laborious, and I managed to get it built for Linux using these
 instructions: http://scelementary.com/2015/04/25/openacc-in-gcc.html The
 instructions are for GCC 5.0 but they work fine for 6.1.

 In short, an external assembler for PTX is built, then GCC is configured,
 built and installed targeting PTX. Then GCC is built for the second time,
 configured as a host compiler specifying that it can offload.

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Ticket URL: <https://trac.macports.org/ticket/51367#comment:3>
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