Fix meridian type in getdate.y

Fix meridian type in getdate.y

Commit d3356bc42191c1896ab06835a2fb245e00471420 (ticket 8927)
incorrectly tagged tMERIDIAN as <Number>.  So while the lexer assigns
meridian values to the Meridian union field, the parser erroneously
reads them from the Number field.  On 64-bit IBM zSystems (s390x),
this can result in using the most recently read number as a meridian
value, leading to an abort in ToSeconds().

Fix the tMERIDIAN token type to be <Meridian>.

[ghudson@mit.edu: edited commit message]

(cherry picked from commit 0108d7d7fbb1111c062ac580e69e97103662fc2b)

ticket: 9087
version_fixed: 1.20.2