Comment 7 for bug 1432497

Created attachment 35077
Fix dependencies in go tool for gccgo

The code to determine when to import packages was not quite catching the cases it should. It really needs to know what packages are part of the GO standard packages and not try to load those -- if they aren't then they should be loaded.

This makes a few changes to the previous:
- change the name of reqPkgSrc to reqStdPkgSrc to indicate when we should require the source for GO standard packages when loading packages.
- generate the list of standard packages found in libgo and make that available to build into the go tool
- set the flag Standard in the Package structure correctly for gccgo, based on the list of expected libgo standard packages
- use the reqStdPkgSrc flag and the package.Standard flag to determine if the load of the package should be attempted