Add builtin constants ‘langVersion’ and ‘nixVersion’

The integer constant ‘langVersion’ denotes the current language
version.  It gets increased every time a language feature is
added/changed/removed.  It's currently 1.

The string constant ‘nixVersion’ contains the current Nix version,
e.g. "1.2pre2980_9de6bc5".

1 files changed, 3 insertions, 0 deletions

diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index d25ee6adca30..953eed9c36a2 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -190,4 +190,7 @@ private:
 extern Settings settings;
 
 
+extern const string nixVersion;
+
+
 }