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

make-revision

@@ -0,0 +1,9 @@
+#!/bin/sh
+
+echo "// This header is generated by the make-revision script."
+echo "// For the version, it uses the latest git tag followed by the number of commits."
+echo "// For the date, it uses the current date (when then script is run)."
+
+echo
+echo \#define GLSLANG_REVISION \"`git describe --tags --abbrev=0`.`git log --oneline | wc -l`\"
+echo \#define GLSLANG_DATE \"`date +%d-%b-%Y`\"