Merge pull request KhronosGroup#88 from mgadams/unistd_removal

Remove obsolete unistd.h file

Backward incompatible: Turn on PureOperatorBuiltins: use only enum-ba…

…sed built-in functions in the AST.

If this breaks your AST consumer, best is to modify it to test
against the enum values instead of doing string comparisons on
built-in function names.  This is the reason the change was made.

If you need the old behavior, you should be able to get it back by changing
PureOperatorBuiltins to be false instead of true.  This path will work for
a while, but is marked deprecated.

Also, the old behavior is tagged as release 2.4.

Create last version before moving to pure enums for built-in functions.

Last version of SPIR-V 30, before going to SPIR-V 31.

Version reporting: Restart active use of revision.h, now based on a g…

…it tag.

The new make-revision script regenerates glslang/Include/revision.h,
used as it always has been, but made with a git-tag version and the
the number of commits on master.

I have a pre-commit hook that will automatically do this on master,
likely often enough to work in practice, without needing pull requests
to include it.

Version reporting: Restart active use of revision.h, now based on a g…

…it tag.

The new make-revision script regenerates glslang/Include/revision.h,
used as it always has been, but made with a git-tag version and the
the number of commits on master.

I have a pre-commit hook that will automatically do this on master,
likely often enough to work in practice, without needing pull requests
to include it.