configure: check for python2.7 for PYTHON2

Check for a 'python2.7' binary, 'python' and 'python2' are not
provided by the OpenBSD python 2.7.x packages.

Signed-off-by: Jonathan Gray <jsg@jsg.id.au>
Cc: "11.0 11.1" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
diff --git a/configure.ac b/configure.ac
index 7a3c7cd..adc582b 100644
--- a/configure.ac
+++ b/configure.ac
@@ -98,7 +98,7 @@
 AM_PROG_CC_C_O
 AM_PROG_AS
 AX_CHECK_GNU_MAKE
-AC_CHECK_PROGS([PYTHON2], [python2 python])
+AC_CHECK_PROGS([PYTHON2], [python2.7 python2 python])
 AC_PROG_SED
 AC_PROG_MKDIR_P