Don't redeclare desc in mini_create_ftnptr on ppc64

mini.c: In function 'mini_create_ftnptr':
mini.c:6734:12: error: redeclaration of 'desc' with no linkage
mini.c:6724:12: note: previous definition of 'desc' was here
mini.c:6734:2: warning: ISO C90 forbids mixed declarations and code [-Wdeclaration-after-statement]

(line numbers are slightly out as this was from a 3.2.1 tarball, but the bug remains)