-U__GNUC__ during lint pass

[Gregory McGarry <g.mcgarry%ieee.org@localhost>]

I noticed that lint undefines __GNUC__ during it's pass.  The source  
tree actually requires this to be done.  I added a similar  
undefinition of __PCC__.

But it seems that this may be a hack to avoid auditing the source  
tree and sprinkling some __lint__ tests in the headers.