Commit 0b0d3320 (TCG: Final globals
clean-up) moved code_gen_prologue but forgot to update ppc code.
This broke the build on 32-bit ppc. ppc64 is unaffected.

Cc: Evgeny Voevodin <evgenyvoevodin@gmail.com>
Cc: Blue Swirl <blauwirbel@gmail.com>
Signed-off-by: NAndreas Färber <andreas.faerber@web.de>
Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>