[MacPorts] #62792: legacy-support: rename identifiers that start with underscore

[MacPorts]

#62792: legacy-support: rename identifiers that start with underscore
------------------------+----------------------------
 Reporter:  ryandesign  |      Owner:  cjones051073
     Type:  defect      |     Status:  assigned
 Priority:  Normal      |  Milestone:
Component:  ports       |    Version:  2.6.4
 Keywords:              |       Port:  legacy-support
------------------------+----------------------------
 legacy support uses defines such as:

 {{{
 #if  __MP_LEGACY_SUPPORT_UTIMENSAT__
 }}}

 It is not legal to define identifiers beginning with double underscore,
 and defining identifiers beginning with a single underscore seems bad too.

 https://stackoverflow.com/questions/25090635/use-and-
 in-c-programs#answer-25090719

 > * All identifiers that begin with an underscore and either an uppercase
 letter or another underscore are always reserved for any use.
 > * All identifiers that begin with an underscore are always reserved for
 use as identifiers with file scope in both the ordinary and tag name
 spaces.

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Ticket URL: <https://trac.macports.org/ticket/62792>
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