Bump minimum required Bison version to 2.4

This lets us replace the deprecated `%pure-parser` directive with
`%define api.pure`, and get rid of some other conditional code.

Bison is only required for developers hacking on the grammar, since we
check in the generated code.  Bison 2.4 was released in 2008, and is
included in operating systems as old as Red Hat Enterprise Linux 6.

1 files changed, 1 insertions, 1 deletions

diff --git a/perly.y b/perly.y
index 191341fbec..843a3b18bb 100644
--- a/perly.y
+++ b/perly.y
@@ -31,7 +31,7 @@
 
 /*  Make the parser re-entrant. */
 
-%pure-parser
+%define api.pure
 
 %start grammar